Glutamic oxalacetic aminopherase (transaminase) is widely distributed in animal tissues. Its greatest activity has been found in homogenates of heart muscle, skeletal muscle, brain, liver, and kidney, in decreasing order. This enzyme activity has been found in all animal and human serums tested, and the activities are comparable whether the analysis is done chromatographically or spectrophotometrically. It has been demonstrated that serum glutamic oxalacetic aminopherase activity increases 2 to 20 times normal after acute myocardial infarction and may rise 20 to 100 times normal in hepatitis due to toxic or infectious agents. The present study is an extension of a preliminary report on serum glutamic oxalacetic aminopherase alterations in liver disease, with particular emphasis on hepatitis. The study to be reported will describe the activity in hepatitis and discuss the usefulness of determination of the activity in the diagnosis and management of hepatitis and in the epidemiological course of infectious