Renal complications of sulfadrugs are the result of poor solubility of these drugs in their acetyl derivatives and moreover, there is an intimate relationship between the degree of acetylation and the solubilities of the various sulfa drugs. Experimental studies have shown that sulfadiazine is absorbed rapidly after oral administration, gave relatively high blood concentration, leaves the blood tream slowly with less acetylation, and produced very little toxic reaction on tissues, especially in the urinary tract. In this studies, the author made an experiment of sulfadiazine on rabbits using the renal clearance test and obtained the following results. 1. The amounts of urine, GFR, RPF, RBF, hematocrit showed obviously decreases by the administration of 0.05 g, 0.10 g, 0.20 g per 1 kg weight of rabbits for 10 days. 2. The renal damages paralleled to the amount of sulfadiazine administrated on rabbits and acute renal insufficiency cound be observed.