Paul Hubschmid as John McLaren

Madeleine Fischer as Katy Dandridge

Fiorella Mari as Mary McLaren

Ivo Garrani as Professor Herbert Weisse

Dario Michaelis as Peter Leduq

Sam Galter as Randowsky

Jean-Jacques Delbo as Sergei Boetnikov

Peter Meersman as General van Dorff (uncredited)

Massimo Zeppieri as Dennis McLaren (uncredited)

Annie Bernal as Lab Assistant (uncredited)

Giacomo Rossi Stuart as Stuart (uncredited)

Gérard Landry as Landowsky (uncredited)

Shane Rimmer as John McLaren (uncredited) (voice)