A variant of the Fanconi syndrome is reported in an infant with rickets, hypophosphataemia, severe `proximal' renal tubular acidosis, and generalized hyperaminoaciduria. Noteworthy was the absence of glycosuria and cystinosis. Large doses of dihydrotachysterol (DHT) and of alkali controlled all of these abnormalities. Renal function tests including glomerular filtration rate, renal blood flow, ammonia secretion, titratable acidity, and bicarbonate handling were normal when the child was receiving DHT. At age 4½ years total relapse followed the cessation of therapy, and at this time serum parathyroid hormone levels were not raised. Now DHT alone (without alkali supplement) reversed all of the biochemical abnormalities including the acidosis. This child thus has an apparently vitamin D-dependent `proximal' tubular acidosis, which is not due to secondary hyperparathyroidism.