In the 1950s, the idea of sex change increasingly assumed the mainstay of public interest. As psychiatrists and psychologists developed new understandings of gender, the role of surgeons is often overlooked in the early history of sex reassignment. This article explores the work of one such doctor, Elmer Belt, a urologist based in Los Angeles. Between 1953 and 1962, Belt operated on twenty-nine male-to-female patients in the face of ethical and material obstacles. Working closely with Harry Benjamin, Belt developed a surgical technique that transplanted the testes inside the abdomen rather than involving full castration. He became involved in the famous case of Agnes Torres, on which other high-profile scientists based their invention of such seminal concepts as "passing" and "gender identity." Belt's utilization of Agnes as exemplary evidence to support his technique illustrates how and why testicular retention remained a heated topic in the development of transsexual science.