We performed a prospective study on 68 subjects with biopsy-proven glomerulonephritis using a discriminant analysis of 12 clinical and laboratory characteristics. Among these, the selectivity of proteinuria, the presence of hematuria and the plasma level of C3 proved to be the most useful. An equation based on these three variables discriminated without overlap between 17 patients with minimal change glomerulonephritis (MCGN) and 30 patients with either membranoproliferative or rapidly progressive glomerulonephritis. However, some overlap existed between MCGN and focal sclerosis or membranous glomerulonephritis. In addition, the formula seems to identify steroid-resistant patients with MCGN.