Huge strides have been made in the molecular genetics and clinical investigation of several inherited renal diseases. In autosomal dominant polycystic kidney disease 1) the genetic localization of the defective gene that causes type 1 disease has been narrowed to 500 to 750 kb on chromosome 16; 2) cystogenesis has been associated with increased cell proliferation, continuing cyst secretion, and a defect in cell polarity; however, the mechanisms by which the genetic defects in autosomal dominant polycystic kidney disease translate into cyst formation are unknown; 3) activation of the renin system has been reported as an important potential cause of hypertension; and 4) factors that influence the progression to renal failure have been identified. In Alport's syndrome, mutations in the alpha 5 (IV) collagen gene on the X chromosome have been demonstrated that may induce defective assembly of alpha 3 (IV) chains by an unknown mechanism, which leads to the disruption of the glomerular basement membrane. In diabetic nephropathy, it has been suggested that familial factors, perhaps genetic in origin, may play an important role in its development.