Mechanisms for the citraturic response to potassium citrate treatment were sought by assessing renal citrate clearance and acid-base status after oral administration of potassium citrate, potassium bicarbonate, and potassium chloride. After 2 weeks of treatment of eight patients with stones at a dose of 80 meq/day, urinary citrate rose significantly from 2.5 +/- 1.6 mmol/day (no drug) to 5.1 +/- 1.7 mmol/day with potassium citrate and to 4.5 +/- 1.5 mmol/day with potassium bicarbonate (P less than 0.05), but did not change significantly with potassium chloride. Citrate clearance increased from 8.0 to 27.4 mL/min with potassium citrate and 25.8 mL/min with potassium bicarbonate (P less than 0.05), but did not increase with potassium chloride. Both potassium citrate and potassium bicarbonate significantly raised urinary bicarbonate and decreased urinary ammonium, titratable acid, and net acid excretion. Potassium chloride was without effect. Effects of potassium citrate on urinary citrate, citrate clearance, and acid-base status tended to be more prominent than those of potassium bicarbonate, but these changes were not significant. Thus, the citraturic action of potassium citrate is largely accountable for by provision of an alkali load. Potassium itself had no effect in the absence of potassium deficiency.