735. Treatment of primary hyperoxaluria. Nine patients with primary hyperoxaluria have been followed regularly for 1 to 11 years, and their treatment and progress are discussed in relation to the known natural history of the disease. 6 of them probably have the usual form of primary hyperoxaluria associated with increased glycollic acid excretion, while 3 who are sibs have the recently described variant associated with L-glyceric aciduria and normal glycollic acid excretion.All 9 patients have been on regimens designed to increase the urinary solubility of calcium oxalate, with or without the simultaneous lowering of urinary calcium and raising of urinary phosphate excretions. 8 patients have been treated for 1 -7j years (average duration 4 years) with oral magnesium hydroxide, and 2 patients have been treated with sodium phosphate. One of the latter was changed after 31 years to magnesium hydroxide and the other has been on sodium phosphate combined with a low calcium diet and cellulose phosphate continuously for 5j years. 2, not at first diagnosed as hyperoxalurics, were first given sodium bicarbonate for their presumably secondary renal tubular acidosis.The over-all progress of the whole group is felt to have been better than could be expected from the known natural history of primary hyperoxaluria.