A method of short-term organ culture in chemically-defined media of human mammary carcinoma is described. Hormonally dependent proliferation over a 48-hour period is demonstrable in some human breast carcinomas, and uniform maintenance of the explants was obtained over the 48-hour period of incubation. The method permits routine explanting of an individual patient’s carcinoma in the organ culture system described, and may eventually provide useful information for management of advanced breast carcinoma with appropriate antihormonal therap