A 37 yr old white male, working in a tile factory, presented proteinuria with no obvious tubular dysfunction. Renal biopsy disclosed a mild focal segmental proliferative glomerulonephritis. Distinct alterations were found by EM, especially in the proximal tubular cells. Because of a history of heavy dust exposure the Si content was determined in the kidney biopsy tissue. The finding of 150 mg/kg silicon on tissue dry weight supports the diagnosis of silicon nephropathy.