H. Leslie Moore1recently reported the occurrence of hypertrophic pyloric stenosis in twins. At 4 weeks of age each had a Rammstedt operation. Each did well at first, but this lasted only a few days, and they both died of respiratory paralysis, six and eight days after the operation. Moore states that he has been unable to find any other case of this malady in twins in the literature. He also says that it would be interesting to know whether it ever occurred in one twin and not in the other. In 1919, I observed a similar condition in twin boys, born Oct. 14, 1919, and referred by Dr. Clyde Moore. REPORT OF CASES J., the first infant, did well until 13 days old, when he began to vomit. At that time he vomited practically everything he ate. At birth, he weighed 5 pounds, 12 ounces (2.60 kg.) and