The effects of long-term treatment with potassium citrate, 30 to 80 meq/d over 2.13 +/- 0.76 (SD) years, were examined in 37 patients with "idiopathic" hypocitraturic calcium-oxalate nephrolithiasis, in whom the main causes of hypocitraturia (renal tubular acidosis, chronic diarrhea, urinary tract infection, or hypokalemia) were excluded or considered unlikely. Potassium citrate treatment produced a sustained increase in urinary citrate excretion from initially low values (223 to 253 mg/d) to within normal limits (470 to 620 mg/d). Urinary pH rose significantly and was maintained at 6.5 to 7.0. Along with these changes, urinary saturation of calcium oxalate declined significantly to normal limits. Further stone formation ceased in 89.2% of patients during treatment, and the stone formation rate declined from 2.11 +/- 5.68 to 0.28 +/- 1.30 stones/patient-year (p less than 0.01).