Summary Oral administration of sodium sulfapyridine produces marked gastric irritation and results in rats, rabbits and monkeys in the formation of urinary concretions. The minimal doses necessary to produce these phenomena vary from 0.25 g per kg in monkeys to 2 g per kg in rats, administered daily for 10 days. Larger doses (3 to 4.5 g per kg) may cause urolithiasis even after a single administration.