The relative topical efficacy of indomethacin and diflumidone, a novel non-steroidal antiinflammatory drug, for the suppression of ultraviolet-light (290-320 nm region; UVB)-induced erythema has been compared in a randomized, double-blind, placebo-controlled study in man. During the early phases of erythema development (3-6 h) following the administration of 3 minimal erythema doses (MED) of UVB, a single topical application of diflumidone and of indomethacin were found to be equal in their ability to inhibit the development of erythema compared to untreated or placebo-treated sites. At 24 h after application, the indomethacin-treated sites had significantly less erythema than did the diflumidone-treated sites. Pigmentation of test sites at 5 and 14 days following irradiation was indistinguishable at the diflumidone, placebo, or untreated sites, but relatively less pigment developed at the indomethacin-treated sites.