Peripheral blood T-lymphocytes, studied in 50 patients with pemphigus vulgaris by means of spontaneous (E) and active (EA) rosette-formation, were increased in active disease and gradually returned to normal after achieving clinical remission of pemphigus vulgaris. The portion of B-cells quantified by M-rosette formation was increased in active disease as well (19.9 +/- 3.0% vs. 10.8 +/- 1.6% in controls) (p less than 0.02) but returned to normal immediately after clinical remission was obtained. Levamisole in vitro suppressed E-, EA-, and M-rosette formation in all the patients examined with active disease. The subsets of T-cells in 10 non-treated patients with active pemphigus vulgaris and 5 patients with a long-term steroid maintained remission of the disease were studied using OKT series monoclonal antihuman antibodies. A statistically significant increase in the percentage of OKT3+ cells (p less than 0.05) and a considerable increase in OKT4+ cell count (p less than 0.002) were registered in patients with active pemphigus vulgaris, compared with controls. In five patients with 2-9 years' remission the percentage of OKT3+, OKT4+, OKT5+ and OKT8+ cells did not significantly differ from controls.