Circulating levels of immunoreactive parathyroid hormone were measured in six patients with distal renal tubular acidosis before and during two years of long-term alkali therapy. Parathyroid hormone level was elevated modestly in five patients before treatment and fell, gradually during treatment to normal or near normal levels. Urine calcium level fell, serum calcium level rose, and renal phosphorus reabsorption rose during treatment. Stopping treatment briefly caused reversion of serum parathyroid hormone and calcium levels and renal phosphorus reabsorption to pretreatment values within eight weeks. Mild hyperparathyroidism is present in renal tubular acidosis and reverses with alkali treatment.