During a short period in the summer of 1960 an unusual number of cases of infectious hepatitis was reported to the Connecticut State Department of Health from the town of Brookfield, Conn. The authors undertook an intensive epidemiological investigation of the outbreak. Thirty cases were found to have occurred in 2 months: 21 in July and 9 in August. Of the July cases, 19 were students in the grades 3 to 6 of 1 school. The August cases were all contacts of July cases. Epidemiological evidence implicated, as the vehicle of infection, the water from a well supplying the portion of the school used by the upper grades. Bacteriological evidence gave support to the theory.