Transplantation of tissue from a cribriform human prostatic carcinoma resulted in a serially transplantable tumor line in nude mice, PC 82. During 2 1/2 years the tumor has not changed its histological appearance and remained a moderately differentiated adenocarcinoma. The cells contain large amounts of prostatic acid phosphatase. It has a slow rate of growth and regresses after castration and estrogen treatment. This preliminary information suggests that the PC 82 tumor line may be suitable model for hormone-dependent human prostatic cancer.