Abstract: In the present study the percentage of T lymphocytes, T cell subsets and B cells, defined by anti-human T cell monoclonal antibodies (T3, T4, T8), using indirect immunofluore-scence technique and surface membrane immunoglobulin (SmIg) using direct immuno-fluorescence technique were determined in the peripheral blood of 47 patients with psoriasis vulgaris. By using ¹²⁵IUdR release test for the natural killer (NK) cell activity of peripheral blood mononuclear cell of 22 patients was determined. Normal healthy persons were used as control. The results further support that there is defect of cellular immunity in patients with psoriasis. The authors postulate that the disturbance of immunoregulation in psoriasis, especially the increase of negative immunoregulation, may play a role in the pathogenesis of psoriasis.