Margaret O'Brien

Alpha

James Craig

Mike Regan

Marsha Hunt

Katie Mallory

Philip Merivale

Professor Peter Vincent

Henry O'Neill

Professor Josh Pringle

Donald Meek

Professor Catty

Keenan Wynn

Packy Roost

Alan Napier

Dr. Woodring

Sara Haden

Rhoda Kitterick

Kathleen Lockhart

Mrs. Catty

Howard Freeman

Professor Richards

Walter Fenner

Professor Endicott

Elisabeth Risdon

Mrs. Pringle

Robert Blake

Jerry

Barbara Bedford

Telephone Operator (uncredited)

Roy Rowland