Nine children with proximal renal tubular acidosis and four with distal renal tubular acidosis have been followed for periods ranging from six months to eight years. The patients with proximal renal tubular acidosis, predominantly male, presented with growth retardation and acidemia at ages 2 to 19 months. Treated with high-dose alkali therapy, most of these patients have shown improvement in growth rate. Now, one to eight years after diagnosis, seven of the nine patients are completely normal without therapy. The patients with distal renal tubular acidosis, 2 boys and 2 girls, presented at ages 4 to 13 years with growth retardation, polyuria, and recurrent episodes of acidosis and dehydration. Three had nephrocalcinosis and hypokalemia, and all demonstrated a renal concentrating defect. Three to eight years after diagnosis these patients continue to require low-dose alkali therapy; the renal concentrating defect and nephrocalcinosis persist, although the glomerular filtration rate has normalized.