We have studied a family in which nine members present hyperchloremic acidosis with normal plasma creatinine and good ability to acidify urine. Renal functions, other than bicarbonate wasting, are normal, which identifies the condition as a pure form of proximal renal tubular acidosis. The acidosis persists into adult life and appears to be inherited as an autosomal dominant trait. All affected members are asymptomatic and the only peculiar finding is a decrease in stature. No hypercalciuria was detected, and no evidence of rickets or osteomalacia was found by x-ray studies. We consider these findings characteristic of a familial trait different from that in previously reported cases of renal tubular acidosis.