Ninety-seven men were exposed on the same day to infectious hepatitis in drinking water. One third developed icteric disease, 60% had anicteric disease, and 7% had no evidence of disease. Elevated serum glutamic pyruvic transaminase (SGPT) level was the most frequent chemical abnormality in the anicteric group. Serial measurements of the levels of SGPT, serum glutamic oxaloacetic transaminase (SGOT), ornithine carbamyl transferase (OCT), serum alkaline phosphatase, bilirubin, and cholesterol in the icteric group demonstrate the time course and extent of these abnormalities in this homogeneous population. The levels of serum bilirubin, alkaline phosphatase, and OCT decreased in parallel and were normal by 70 days after exposure. The SGPT and SGOT levels remained elevated longer. At 145 days after exposure, some patients still had elevated SGPT and SGOT levels. Transient hypercholesterolemia occurred in a significant number of patients reaching a maximum 55 days after exposure. The mean value was normal 25