Anthralins, especially dithranol, have been used for the treatment of chronic dermatoses for many years. Unfortunately dithranol stains the skin yellow or brown. It also irritates healthy skin more than psoriatic areas. A new anthralin derivative, butantrone may be tolerated better. Because the skin of the swine resembles human skin in many respects, the Göttingen miniature swine was selected as the test animal for the present study. 12 Göttingen miniature swines of the uncoloured line were randomized into three groups. The two anthralin derivatives were spread in three separate bases (ointment, stick and gel) and in three concentrations each on the allocated skin sites on the flanks of the animals. The responses of the skin were evaluated daily (except Sundays) for six months. Because there was a separate group for the control animals (bases only), for dithranol and butantrone, it was possible to make observations on systemic toxicity, too. Butantrone and dithranol turned out almost equally irritating to the skin of the miniature swine. The mean primary irritation scores in the butantrone group were slightly higher than in the dithranol group. On the other hand, the concentrations of butantrone were higher. It is possible that the release of the drugs from the gel formula was poorer than from the ointment and stick bases.