Sebum production has been measured in twenty patients in whom 13-cis-retinoic acid therapy had been discontinued for at least 20 weeks. While sebum production had returned to pretreatment levels by 30 weeks in seven subjects, 30% to 80% reduction in sebaceous gland activity was still present for as long as 80 weeks in eight subjects. Four of these eight patients, who were followed for more than a year, still had marked sebaceous inhibition when last tested. The prolonged remission seen in patients with nodulocystic acne may be related in part to continued sebaceous gland inhibition in some patients, but it obviously is not the only factor responsible for the long-term improvement that is seen.