Ro 10-9359 is a retl·noic acid derivative, selected for study because of a better tolerance than retinoic acid, shown in animal experiments. Earlier clinical experience has proved Ro 10–9359 to be an extremely potent antipsoriatic drug. The well-known association between psoriasis and pustulosis palmoplantaris was a motivation to evaluate Ro 10-9359 also in the last-mentioned disease, which is notoriously known to be resistant to treatment. In this study 30 patients were given either 75 mg/day of Ro 10-9359 or 200 mg twice every week according to a randomized pattern. All patients had suffered from the disease for at least 2 years without any spontaneous remission during the year preceding the trial. After a treatment period of about 2 weeks with Ro 10–9359 hyper-keratotic scales had usually disappeared, and 2 weeks later there were in general significantly less pustular lesions. The treatment continued for 8 weeks, and at this time the average reduction of the number of pustules was 80%. The daily dosage seemed to give better results and was also better tolerated than was the twice-weekly dosage. Side effects were common, but generally mild. On average, the remission lasted 1 month after cessation of therapy.