Ten psoriatics were tested with three concentrations of butantrone (0.66, 2.0 and 3.9%) on the healthy skin of the back and the irritant and staining reactions were compared with those produced by 0.1 and 0.5% dithranol, both in white petrolatum. Of the three test areas one was stripped before exposure to simulate the penetration of a psoriasis lesion, one after exposure to simulate posttreatment washing and one was unstripped. The contact times were 20 and 60 min. The degrees of erythema and staining, and the increase in skin blood flow were measured 1, 2, 3 and 7 days after application. Both dithranol concentrations produced a markedly stronger increase of blood flow and erythema than any of the butantrone concentrations and a clear dose response when the concentration was raised from 0.1 to 0.5%. Such a dose response was not clearly seen with butantrone. Staining with both dithranol and butantrone was minimal. Apparently, higher concentrations of butantrone than dithranol can be used in short contact therapy if cumulation of the drug can be excluded by a short contact time and careful removal of the surplus drug.