Mary Martin's designer of choice was Mainbocher. He was brought in at her request to design her costumes, although he ended up not designing all of them. Lucinda Ballard, who designed the costumes worn by everyone else in the production, was credited with designing Martin's postulant costume and her last two costumes.
When Martin left the show, the Mainbocher costumes did too. They were replaced by costumes designed by Ballard. Florence Klotz was Ballard's assistant.