Since its introduction, the effectiveness of dithranol in treating psoriasis has been unequalled by other topical treatments. Out-patient short-contact dithranol treatment is effective with regard to clinical response rate and relapse rate after 1 year. A drawback, however, is the relatively long treatment duration. To study a dithranol regimen combined with a potent topical corticosteroid with regard to clinical response rate, treatment duration and remission period after clearance. Twelve patients with stable psoriasis vulgaris participated in this study. We treated three comparable psoriasis lesions on the extremities for 39 consecutive days. The first lesion was treated daily with short-contact dithranol cream followed by clobetasol-17-propionate ointment 5 days per week. The second lesion was treated daily with short-contact dithranol cream followed by the vehicle of clobetasol-17-propionate ointment. The third lesion was treated with clobetasol-17-propionate ointment 5 days per week. The patients attended on days 1, 4, 9, 12, 15, 18, 22, 25, 32 and 39 during treatment. We assessed lesional severity scores at each visit and registered the baseline area at the first visit. During the follow up at weeks 2, 4, 6, 10, 14, 19 and 23 we assessed lesional sum scores. We also estimated the area involved in recurrence of the lesion as a percentage of the baseline area. The overall differences between the three treatment curves for the treatment period and follow-up period separately were tested with a likelihood ratio test. Differences between the curves of the sum scores during treatment (P < 0.001) were mainly due to the different time-course of dithranol monotherapy, which showed a slower decrease in sum score. Differences between the linear trends of the sum score (P < 0.001) and the area score P < 0.001) during follow up were due to a different time-course of the combination therapy, which started lower and increased more slowly, suggesting a slower relapse rate with combination therapy. When comparing the follow-up data, it must be kept in mind that the three treatments showed an overall significantly different sum and area score at the start of follow up. Intermittent addition of clobetasol-17-propionate ointment enhanced the antipsoriatic efficacy of short-contact, high-dose dithranol therapy in terms of clearing capacity and treatment duration, without shortening remission duration.