Five children who have evidence of residual nephritis after an episode of acute poststreptococcal glomerulonephritis have been investigated to determine the relationship of their disease to membranoproliferative nephritis. Measurements of serum β1C-globulin and study of late renal biopsies showed no changes suggestive of membranoproliferative disease. Serum β1 levels were normal, and silver staining of renal biopsies gave no evidence of deposition of large quantities of nonargyrophilic material typically observed in membranoproliferative nephritis.