Hepatic gamma-cystathionase activity at 12 h after the intraperitoneal injection decreased in proportion to the amount of D,L-propargylglycine administered, but hepatic cystathionine beta-synthase activity did not change. Contents of cystathionine in the liver increased gradually from 0.25 mg to 30 mg/200 g body weight in proportion to the amounts of D,L-propargylglycine injected; in the kidney, 0.5 mg to 10 mg; in the brain, 5 mg to 20 mg; in the serum, 0.25 mg to 30 mg. Contents of N-acetylcystathionine in the liver and kidney also increased in parallel with the accumulation of cystathionine.