George Sanders as Gen. Armstrong

Maurice Evans as Dr. Matthews / Alien

Patrick Allen as Bob Megan

Neil Connery as Jim Radford

Robert Flemyng as W.C. Baldwin

Pamela Conway as Lorna

Allan Cuthbertson as Hindsmith

Michael Culver as Lt. Bailes

Sally Faulkner as Joanna

Shelagh Fraser as Mrs. Thatcher

Hilary Dwyer as Julie Slade

Dennis Chinnery as Control Officer