George C. Scott as Dan Charles Logan

Richard Basehart as Dr. Roy Caldwell

Martin Sheen as Maj. Holliford

Barnard Hughes as Dr. Spencer

Nicolas Beauvy as Chris Logan

Paul Stevens as Col. William Franklin

Stephen Young as Major Reintz

Kenneth Tobey as Col. Alan A. Nickerson

Robert Walden as Dr. Janeway

William Jordan as Major Cooper

Dabbs Greer as Dr. Thompson

John Dierkes as Bill Parker

Bette Henritze as Sarah Parker

Lou Frizzell as Dr. Spike Boynton

Ed Lauter as Simpson

Phoebe Noel as Waitress

Steve DeFrance as Ambulance Driver (uncredited)

Anna Aries as Bit Part

Fielding Greaves as Dr. Walter Steenrod, Chivington Research Laboratories

Terry Wilson as Kaufman Trucking Co. driver