Fifteen (15) patients diagnosed of adult renal polycystosis with normal renal function (creatinine clearance) greater than 80 cc(min/1.73 m2 c.s.) were studied in order to assess distal renal tubular functioning. We observed a great variation in the data obtained, 6 patients with disorders in the concentration capacity (40%); 5 patients (33%) with defects in ammoniogenesis and in net excretion of acids; 3 patients (20%) with isolated ammoniogenesis defects and 6 patients (40%) without any functional disorder. Given that there were patients (6) without distal tubular disorders, these studies should not be used as diagnostic method of adult renal polycystosis.