Nine patients who developed proteinuria while on Tiopronin (a D-Penicillamine-like drug) have been studied. Nephrotic syndrome was observed in six cases. Immunologic analysis revealed a high frequency of ANA positivity and RF seronegativity by the time nephropathy appeared. Six patients were biopsied. Immunofluorescence, electron and light microscopy studies showed: glomerulonephritis with segmental deposits in the mesangium and along the capillary walls in one patient, mesangioprolipherative glomerulonephritis in one case and stage 1 membranous glomerulonephritis in four cases. Immunogenetic typing disclosed a strong association with B35-Cw4 class I antigens.