In 44 patients with chronic plaque psoriasis anthralin therapy was used as high-strength short-contact therapy in a bilateral comparison of anthralin versus 5% crude coal tar-anthralin combination. These two trials were undertaken with and without ultraviolet (UV) irradiation immediately after anthralin therapy. The combined tar-anthralin therapy was significantly less of an irritant during the first 3 weeks of treatment than anthralin alone, and it did not decrease the antipsoriatic efficacy. The use of UV irradiation, either with anthralin or tar-anthralin combination, did not produce an additional therapeutic effect. These findings lead us to prefer combined tar-anthralin therapy because of its lower irritancy in comparison with anthralin alone and they show the ineffectiveness of additional UV irradiation under the conditions of this study.