Serum concentrations of IgG, IgM and complement components C3 and C4 were estimated in thirty-one adult Nigerian patients with nephrotic syndrome; twenty-eight of whom had 'active' disease, while three were in remission. Eleven normal adults served as controls. The mean serum IgG was significantly lower, while the mean serum IgM was higher in the patients with active disease than in the controls. Similarly mean serum C3 and C4 levels were statistically significantly higher (P less than 0.05) in active disease than in normal controls. These findings in Nigerian patients are similar to those observed in Caucasians, and further support the role of a fundamental immunological defect in the pathogenesis of the nephrotic syndrome.