The effects of thymus factor (TFX) and levamisole on the clinical picture and some indices of cellular immunity have been evaluated in 10 patients with nephrotic syndrome due to membranoproliferative glomerulonephritis Type I. The patients revealed decreased T-lymphocyte number and impaired responsiveness to phytohaemagglutinin (PHA) stimulation before treatment. An association between the slight diminution of proteinuria and the increase of E-rosette forming lymphocytes, increased responsiveness to PHA and return to normal of previously elevated B-cell percentages, was observed in four patients treated with TFX and one patients treated with levamisole.