THE GENERAL hospital in which I served during the war cared for 2,346 patients with infectious hepatitis in the course of a two year experience in the Mediterranean Theater. Of the 956 cases seen in the first three and one-half months, 680 involved British personnel admitted from a staging area which also furnished many cases of diarrheal disease. The parallelism between the incidence curves of diarrheal disease and infectious hepatitis was so close that it became the firm conviction of my associates and me that the answer to the question of causation of the latter disease was, in this instance at least, one of sanitation. We were forced to wait a year and a half, however, before an opportunity was offered to put our convictions to a clearcut test. During April 1945 a number of patients with hepatitis with jaundice were admitted from one battalion of an infantry regiment in