Status of basement membrane antigens in renal polycystic disease was investigated. Antibodies directed against various components of basement membrane, including anti-heparan sulfate proteoglycan, Type IV collagen, laminin, and fibronectin, were employed. Their reactivities with basement membranes of normal and cystic segments of the renal tubules were ascertained by indirect immunofluorescence. The tissues were obtained either from kidneys of patients with adult (autosomal dominant) polycystic disease or from rats with renal cystic change induced by administration of 2-amino-4,5-diphenylthiazole HCl. The human and rat tissues that had undergone cystic change exhibited essentially similar results. A loss of reactivity to anti-heparan sulfate proteoglycan antibodies was observed. The reactivity toward anti-Type IV collagen and laminin either remained unchanged or was focally increased. The reactivity toward fibronectin, normally absent, increased dramatically in the peritubular regions and interstitium. The results indicate that there is an imbalance in various antigenic components associated with renal tubular cystic disease in rat and man, which may have a fundamental role in the pathogenesis of this disorder.