The results of immunoperoxidase staining of 33 routinely processed renal biopsies correlated with the results of direct immunofluorescence in 79% of tests performed. Most of the discrepant results were due to positive immunoperoxidase staining, possibly reflecting greater sensitivity of the method. A comparison of two immunoperoxidase methods showed that the indirect method produced less intense staining than the peroxidase-antiperoxidase (PAP) method when equivalent primary antibody titres were used. Lowering the primary antibody titres for the indirect technique resulted in equivalent staining by the two methods. Predigestion by protease VII effectively revealed the antigens under study without causing tissue damage or section loss.