The effect of fluocinonide ointment and 5% crude coal tar on clearance of plaque-type psoriasis vulgaris by phototherapy was studied in 25 hospitalized patients using the bilateral comparison technique. All treated areas received ultraviolet radiation from Westinghouse fluorescent FS-40 bulbs (290-400 nm) in doses calculated to produce a minimal delayed erythema. The topically applied compounds (fluocinonide ointment, 5% Crude coal tar, white petrolatum) were applied individually or in combination. In nearly all comparisons clearance of psoriatic plaques was obtained after the same number of ultraviolet exposures, although many (8 or 14) of the areas treated with fluocinonide ointment had an accelerated early response. It thus appears that although the use of topical corticosteroids may enhance the early therapeutic response of psoriatic plaques it does not hasten the clearance of these plaques.