This study deals with 13 patients who volunteered for serial biopsies during proquazone treatment which proved to be effective in the majority of the cases. The immunocompetent cells in the inflammatory cell infiltrates were characterized by a panel of monoclonal antibodies: OKT11, OKT4, OKT8, OKT6, NK-9 and Leu-14. Before proquazone treatment there was only a slight predominance of OKT4-positive cells as compared to OKT8-positive cells but a rather high number of NK-9-positive natural killer or activated cytotoxic T cells. The pattern of inflammatory cell subclasses changed during the treatment and the most striking difference was the reduction in the number of the NK-9-positive cells. It is proposed that Jessner’s lymphocytic infiltration of the skin (LIS) should be viewed as an entity and that proquazone possibly acts by modulating the pattern and activation stage of lymphocyte subclasses in LI