Familial nephronophthisis is one of the inherited human cystic kidney diseases and is characterized by progressive renal failure. We have investigated abnormalities of cell-matrix interactions using immunocytochemistry and electron microscopy in three renal biopsies from two patients with familial nephronophthisis and compared our findings to those seen in thirty other renal biopsies. We found expression of the alpha 5 integrin fibronectin receptor in all three samples of nephronophthisis but in no other renal diseases. There was also enhanced expression of the alpha 2 integrin in nephronophthisis but this appeared to be a common response to tubular injury. Electron microscopy showed thickening of the tubular basement membrane and a loss of organization of the basal pole of tubular epithelium. We conclude that altered cell-substratum adhesion contributes to the pathogenesis of nephronophthisis.