| Resigned December 31, 1977, after becoming Deputy Mayor of New York City. Elected on the Republican and Liberal tickets on February 14, but officially took office as a Democrat after being accepted by the caucus on February 21. | nowrap | Robert Garcia (D) | February 21, 1978 |- | | nowrap | Clifford Allen (D) | style="font-size:80%" | Died June 18, 1978 | rowspan=19 |Vacant | rowspan=19 |Not filled this term |- | | nowrap | William M. Ketchum (R) | style="font-size:80%" | Died June 24, 1978 |- | | nowrap | Ralph Metcalfe (D) | style="font-size:80%" | Died October 10, 1978 |- | | nowrap | Goodloe Byron (D) | style="font-size:80%" | Died October 11, 1978 |- | | nowrap | Leo Ryan (D) | style="font-size:80%" | Murdered by members of the Peoples Temple at the Guyana Airport November 18, 1978, shortly before the Jonestown Massacre |- | | nowrap | William A. Steiger (R) | style="font-size:80%" | Died December 4, 1978 |- | | nowrap | Max Baucus (D) | style="font-size:80%" | Resigned December 14, 1978, after being appointed to the U.S. Senate having already been elected. |- | | nowrap | Thad Cochran (R) | style="font-size:80%" | Resigned December 26, 1978, after being appointed to the U.S. Senate having already been elected. |- | | nowrap | Teno Roncalio (D) | style="font-size:80%" | Resigned December 30, 1978 |- | | nowrap | John E. Moss (D) | style="font-size:80%" | Resigned December 31, 1978 |- | | nowrap | John J. McFall (D) | style="font-size:80%" | Resigned December 31, 1978 |- | | nowrap | Del M. Clawson (R) | style="font-size:80%" | Resigned December 31, 1978 |- | | nowrap | Joe Skubitz (R) | style="font-size:80%" | Resigned December 31, 1978 |- | | nowrap | Elford Albin Cederberg (R) | style="font-size:80%" | Resigned December 31, 1978 |- | | nowrap | Joseph A. LeFante (D) | style="font-size:80%" | Resigned December 31, 1978 |- | | nowrap | James J. Delaney (D) | style="font-size:80%" | Resigned December 31, 1978 |- | | nowrap | Olin E. Teague (D) | style="font-size:80%" | Resigned December 31, 1978 |- | | nowrap | William R. Poage (D) | style="font-size:80%" | Resigned December 31, 1978 |- | | nowrap | Omar Burleson (D) | style="font-size:80%" | Resigned December 31, 1978 |} Committees Senate Aging (Special) (Chair: Frank Church) Agriculture, Nutrition