 | Cliff Robertson als Charlie Gordon |
 | Claire Bloom als Alice Kinian |
 | Lilia Skala als Dr. Anna Straus |
 | Leon Janney als Dr. Richard Nemur |
 | Ruth White als Mrs. Apple |
 | Dick Van Patten als Bert |
 | Edward McNally als Gimpy |
 | Barney Martin als Hank |
| William Dwyer als Joey |
| Dan Morgan als Paddy |
| Marianna Case als Young Woman (uncredited) |
| Leon Collins als Tap Dancer (uncredited) |
| Harry Cooper als Conference Attendee (uncredited) |
| Frank Dolan als Eddie (uncredited) |
 | Randee Lynne Jensen als Woman (uncredited) |
 | Ralph Nelson als Convention Speaker (uncredited) |
| Donald Warnock als Conference Attendee (uncredited) |
| Stirling Silliphant | Screenplay |
| Ralph Nelson | Director |
| Daniel Keyes | Novel |
| Selig J. Seligman | Executive Producer |
| Ravi Shankar | Music |
| Ralph Nelson | Producer |
| Arthur J. Ornitz | Director of Photography |
| Fredric Steinkamp | Editor |
| John DeCuir | Production Design |
| Charles Rosen | Art Direction |
| Hazel Roy | Costume Design |
| Vin Kehoe | Makeup Artist |
| Phil Naso | Hairstylist |
| Henry Spitz | Production Manager |
| Tom Walker Jr. | Production Supervisor |
| Shelley Bartolini | Scenic Artist |
| Clem Portman | Recording Supervision |
| Jim Shields | Sound Recordist |
| Jack Brown | Assistant Camera |
| Rod Stephens | Post Production Assistant |
| Richard Kuhn | Title Designer |
