Lee Van Cleef as Dr. Tom Anderson

Beverly Garland as Claire Anderson

Peter Graves as Dr. Paul Nelson

Sally Fraser as Joan Nelson

Russ Bender as General James Pattick

Jonathan Haze as Pvt. Miguel Ortiz

Dick Miller as Sgt. Neil

Paul Harbor as Floyd Mason

Charles B. Griffith as Dr. Pete Shelton

Karen Kadler as Ellen Peters

Taggart Casey as Sheriff N.J. Shallert

Thomas E. Jackson as George Haskell

Marshall Bradford as U.S. Secretary Platt

David McMahon as Gen. Carpenter

Paul Blaisdell as The Monster (uncredited)