Michael Sarrazin as Peter Proud

Jennifer O'Neill as Ann Curtis

Margot Kidder as Marcia Curtis

Cornelia Sharpe as Nora Hayes

Paul Hecht as Dr. Samuel Goodman

Tony Stephano as Jeff Curtis

Norman Burton as Dr. Frederick Spear

Anne Ives as Ellen Curtis

Debralee Scott as Suzy

Steve Franken as Dr. Charles Crennis

Fred Stuthman as Pop Johnson

Lester Fletcher as Car Salesman

Paul Nevens as Room Clerk

Breanna Benjamin as Miss Hagerson

Addison Powell as Reeves

Phillip Clark as Number Five

Gene Boland as Charlie

Albert Henderson as Police Sergeant

Connie Garrison as Ellie

Sam Laws as Satan's Disciple

Mary Margaret Amato as Nurse

Terry Green as College Student

Jacqueline Manning as Lab Assistant

Henry Cosimini as Square Dance Caller

Douglas Rutherford as Club Steward

Marjorie Eaton as Astrology Lady (as Marjorie Morley Eaton)

Shelley St. Clair as Bookstore Clerk

Jon Richards as Newspaper Custodian