Distal renal tubular acidosis is a common cause of intractable calcium nephrolithiasis. We examined the effect of oral potassium citrate therapy in 9 patients with incomplete distal renal tubular acidosis diagnosed on the basis of an abnormal response to an oral ammonium chloride load. Patients were studied during a control phase and after 3 months of potassium citrate treatment (60 to 80 mEq. daily). Potassium citrate caused a significant increase in urinary pH and urinary citrate, and a decrease in urinary calcium. The urinary relative saturation ratio of calcium oxalate significantly decreased during treatment, while that of brushite did not change. Potassium citrate also was shown to inhibit new stone formation. During a mean treatment period of 34 months none of the 9 patients had new stones, although 39.3 plus or minus 79.7 (standard deviation) stones per patient formed during the 3 years preceding treatment. The results support the potential clinical advantage of potassium citrate therapy in patients with distal renal tubular acidosis and recurrent calcium nephrolithiasis.