| Incumbent | Party | Office | Reason for not seeking re-election |
| California |
| Congressman Doug Ose | Republican | House CD 3 | Open Seat. May 2003: Congressman Ose announced that he is retiring and would not run for re-election in 2004. |
| Congressman Calvin "Cal" Dooley | Democrat | House CD 20 | Open Seat. On 2 September 2003, seven-term Democratic Representative Cal Dooley announced that he is retiring and will not seek re-election. |
| Colorado |
| Senator Ben Nighthorse Campbell | Republican | Senate Class 3 | Open Seat. On 3 March 2004, Senator Campbell announced he would not be seeking re-election to a third term. |
| Congressman Scott McInnis | Republican | House CD 3 | Open Seat. 8 September 2003: Six term Congressman McInnis is retiring and will not seek re-election in 2004. |
| Florida |
| Senator Bob Graham | Democrat | Senate Class 3 | Open Seat. 27 February 2003 Senator Graham filed papers to form a Presidential campaign committee and will not be running for re-election to the Senate, 6 October 2003 dropped out of the Presidential contest, 3 November 2003 announced retirement from the Senate. |
| Congressman | Republican | House CD 14 | Vacant Office |
| Congressman Peter R. Deutsch | Democrat | House CD 20 | Open Seat. Ran for, but did not receive, his party's nomination for the Senate in 2004. |
| Georgia |
| Senator Zell Miller | Democrat | Senate Class 3 | Open Seat. 8 January 2003: Senator Miller, 70, announced that he will not seek re-election in 2004. |
| Congressman Denise L. Majette | Democrat | House CD 4 | Open Seat. Running for the Class 3 Senate Seat in 2004 |
| Congressman Johnny Isakson | Republican | House CD 6 | Open Seat. Running for the Senate in 2004. |
| Congressman Michael A. "Mac" Collins | Republican | House CD 8 | Open Seat. Ran for, but did not receive his party's nomination for the Senate Class 3 seat in 2004. |
| Illinois |
| Senator Peter G. Fitzgerald | Republican | Senate Class 3 | Open Seat. 2003 April 15: Senator Fitzgerald announced that he will not seek re-election in 2004. |
| Congressman William O. Lipinski | Democrat | House CD 3 | Open Seat. After being renominated in the 16 March 2004 Primary, on 13 August Congressman Lipinski announced his retirement effective at the end of his current term. |
| Kentucky |
| Congressman Ken Lucas | Democrat | House CD 4 | Open Seat. 24 November 2003: Congressman Lucas announced he will not seek re-election in 2004. |
| Louisiana |
| Senator John B. Breaux | Democrat | Senate Class 3 | Open Seat. 15 December 2003. Senator Breaux announced that he will not run for re-election. |
| Congressman David Vitter | Republican | House CD 1 | Open Seat. Running for Senate in 2004 |
| Congressman W.J. "Billy" Tauzin | Republican | House CD 3 | Open Seat. On 4 February 2004, announced that he will not seek re-election. |
| Congressman Chris John | Democrat | House CD 7 | Open Seat. Running for the Class 3 Senate seat in 2004 |
| Michigan |
| Congressman Nick Smith | Republican | House CD 7 | Open Seat. Retiring. Not a candidate for re-election in 2004. |
| Missouri |
| Governor Bob Holden | Democrat | Governor | Lost Primary. 3 August 2004 |
| Congressman Richard A. Gephardt | Democrat | House CD 3 | Open Seat. Running for President in 2004. Not a candidate for re-election. On 20 January 2004, the Congressman dropped out of the Presidential race after a 4th place showing in the Iowa caucuses. |
| Congressman Karen McCarthy | Democrat | House CD 5 | Open Seat. On 22 December 2003 Congressman McCarthy announced she is retiring. |
| Montana |
| Governor Judy Martz | Republican | Governor | Open Chair. 13 August 2003: Governor Martz announced that she will not run for re-election in 2004. |
| Nebraska |
| Congressman | Republican | House CD 1 | Vacant Office. Republican Congressman Doug Bereuter resigned from the House of Representatives effective at the close of business on 31 August 2004. On 16 December 2003 the congressman announced that he would not seek re-election in 2004. |
| New York |
| Congressman Jack Quinn | Republican | House CD 27 | Open Seat. Retiring. Not a candidate for re-election. |
| Congressman Amory R. "Amo" Houghton, Jr. | Republican | House CD 29 | Open Seat. Retiring. Not a candidate for re-election. |
| North Carolina |
| Senator John Edwards | Democrat | Senate Class 3 | Open Seat. Sunday 7 September 2003: Senator Edwards, a contender for the 2004 Democratic presidential nomination, announced that he will not seek re-election to the Senate in 2004.
Tuesday 6 July 2004: Senator Edwards was named by presumptive Democratic presidential nominee Senator John Kerry of Massachusetts to be his running mate. |
| Congressman Richard M. Burr | Republican | House CD 5 | Open Seat. Candidate for Class 3 Senate seat in 2004. |
| Congressman T. Cass Ballenger | Republican | House CD 10 | Open Seat. Announced retirement 2 December 2003. |
| Oklahoma |
| Senator Don Nickles | Republican | Senate Class 3 | Open Seat. 7 October 2003: Senator Nickles announced that he will not seek re-election in 2004. |
| Congressman Brad Carson | Democrat | House CD 2 | Open Seat. Running for the Senate in 2004. |
| Pennsylvania |
| Congressman Jim Greenwood | Republican | House CD 8 | Open Seat. Announced retirement on 22 July 2004. No longer a candidate for relection. |
| Congressman Joseph M. Hoeffel | Democrat | House CD 13 | Open Seat. Running for Senate in 2004. |
| Congressman Pat Toomey | Republican | House CD 15 | Open Seat. Ran for, but lost, the nomination for Senate in 2004. |
| South Carolina |
| Senator Ernest F. "Fritz" Hollings | Democrat | Senate Class 3 | Open Seat. 4 August 2003: Senator Hollings, 81, announced that he will retire at the end of his current term. |
| Congressman Jim DeMint | Republican | House CD 4 | Open Seat. Running for Senate in 2004. |
| Texas |
| Congressman Jim Turner | Democrat | House CD 2 | Open Seat. 6 January 2004: Congressman Turner announced that he would not seek re-election due to redistricting. |
| Congressman Chris Bell | Democrat | House CD 25 | Lost Primary. in new CD 9 [9 March 2004] |
| Congressman Ciro D. Rodriguez | Democrat | House CD 28 | Lost Primary. 9 March 2004 |
| Utah |
| Governor Olene S. Walker | Republican | Governor | Failed to qualify for Primary. not among the top two contenders in delegate voting on the Gubernatorial nomination at the 8 May 2004 Republican State Convention |
| Virginia |
| Congressman Edward L. "Ed" Schrock | Republican | House CD 2 | Open Seat. Renominated by Primary on 8 June 2004 but announced his retirement and withdrew on 30 August 2004. |
| Washington |
| Governor Gary Locke | Democrat | Governor | Open Chair. 21 July 2003: Governor Locke announced that he will not seek re-election in 2004. |
| Congressman George R. Nethercutt | Republican | House CD 5 | Open Seat. Running for the Class 3 Senate Seat in 2004. |
| Congressman Jennifer Dunn | Republican | House CD 8 | Open Seat. On 30 January 2004, Congressman Dunn announced that she would not seek re-election in 2004. |
| West Virginia |
| Governor Robert E. Wise, Jr. | Democrat | Governor | Open Chair. 12 August 2003: Governor Wise announced that he is not a candidate for re-election in 2004 (issue with marital infidelity). |
| Wisconsin |
| Congressman Jerry Kleczka | Democrat | House CD 4 | Open Seat. On 25 January 2004, Congressman Kleczka announced that he would not seek re-election in 2004. |