Anapsos, an antipsoriatic drug, was administered to normal volunteers in order to study its possible activity on the immune system. After three days of treatment, the drug decreased the lymphoblastic response to PWM and very slightly reduced the serum levels of immunoglobulins. After five days of treatment, however, both values were normal. The response to ConA decreased, and there was an increase in the suppressor index and in the proportion of OKT 8+. The drug did not vary the proportion of OKT 4+ and OKT 3+ cells. These results suggest that anapsos acts by increasing the number of suppressor cells. Such anapsos-induced suppressor cells are probably responsible for the diminished response to ConA, but did not seem to significantly affect response to PWM and serum levels of Ig after five days of treatment.