Peter Cushing as Dr. Brian Stanley

Edward Judd as Dr. David West

Carole Gray as Toni Merrill

Eddie Byrne as Dr. Reginald Landers

Sam Kydd as Constable John Harris

Niall MacGinnis as Mr. Roger Campbell

James Caffrey as Peter Argyle

Liam Gaffney as Ian Bellows

Keith Bell as Halsey

Margaret Lacey as Old Woman

Peter Forbes-Robertson as Dr. Lawrence Phillips

Shay Gorman as Morton

Richard Bidlake as Carson

Edward Ogden as Helicopter Pilot

Joyce Hemson as Mrs. Bellows

Roger Heathcott as Dunley