Hancock, who had worked as a theater director prior, cast the film largely through his connections within the New York theater community, and the majority of the cast consisted of actors with whom Hancock had worked in stage productions. Auditions for the parts were held in the B.S. Moss Offices on Broadway in New York City. Actress Zohra Lampert was cast in the lead role of Jessica, the titular character who finds herself questioning her sanity. She was approached by Hancock, her former boyfriend, while performing in a Broadway production of "Mother Courage and Her Children" with Anne Bancroft. "I accepted, trusting his judgement," Lampert recalled. "I have a great fondness for John Hancock, and enjoyed working with him very much." Lampert "got lost in her character" as the script resonated with her, and she spent much of her time between takes remaining in character. Hancock recalled of her casting: "I knew she would be perfect for the lead role. Zohra could play the fragility of the character, but she could also authentically convey the fear and the terror."