A prospective, randomized, double-blind, placebo-controlled trial was performed to assess the effect of a potent topical corticosteroid cream used in conjunction with ultraviolet B (UVB) phototherapy on psoriasis with respect to time to clearing and duration of remission after clearing. Of the 53 outpatients who received suberythemogenic UVB phototherapy three times per week, 24 applied the topical corticosteroid and 29 applied the placebo cream twice daily until clearing was achieved. Nine patients in each group failed to comply with the protocol. Although there was a trend toward a slightly more rapid response in the topical corticosteroid-treated group, there was no significant difference in patients' early response to therapy, number of treatments, and UVB dose required to achieve clearing. Patients in the topical corticosteroid-treated group remained in remission longer than did patients in the control group (183 vs 116 days). Life-table analysis predicts that 62% of emollient-treated patients flare within 6 months of clearing compared with only 42% of topical corticosteroid-treated patients (p less than 0.1). For most patients with psoriasis who receive UVB therapy in an outpatient setting, the use of potent topical corticosteroids appears to produce, at most, a modest beneficial effect.