The effects of etretinate treatment on natural killer cell activity, on angiogenic capability of peripheral blood mononuclears and on neutrophil adherence were studied in 20 patients with various forms of psoriasis. In all forms of active psoriasis, etretinate was found to affect first the angiogenic reaction and PMN adherence, whereas NK cell activity usually normalized only after a long-term therapy. The earliest normalization of all three parameters was noticed in pustular psoriasis, and it was correlated with the clinical improvement. In two cases of palmo-plantar pustular psoriasis, in 5 cases of arthropathic variety, and in 5 cases of common psoriasis, the normalization preceded clearing of the skin lesions.