Sebum production has been studied in a group of eight elderly patients before and for one year after orchiectomy. A significant decrease in sebum production was observed in the six patients who had a bilateral orchiectomy performed for adenocarcinoma of the prostate gland. The decrease was evident in one month. During a one-year follow-up, these patients demonstrated a slight to moderate increase in sebum production from the initial low values observed in the early months after castration. The other two patients had only a unilateral orchiectomy. In one patient, the ablation of a functional testis caused a reduction in sebum output, but in the other patient no significant change occurred following the removal of an atrophic testis.