William Shatner
— Prof. Stephen Turner
Lynn Carlin
— Barbara
Ossie Davis
— Reed
Viveca Lindfors
— Mrs. Schnagel
Estelle Parsons
— Crossland
Roy Poole
— Dr. Goodman
Mike Kellin
— Mancuso
Richard McKenzie
— Mr. Dennison
Fred J. Scollay
— Dr. McBride
Stephen Macht
— Dahlquist
Lindsay Crouse
— Karen
Charles White
— Harry Vogel
Gregory Abels
— Lab Technician
Robert Burr
— Mr. Hughes
Tom Quinn
— Bully in Bar
Billie Lou Watt
— Mrs. Carol
Michael Howard
Jeff Pomerantz
— Professor
Damon Evans
W.T. Martin
— Mario, the Waiter
Gary Cookson
— Lab Technician
John Travolta
— Lab Technician (uncredited)