In a prospective study of 50 recipients of HBsAg-negative blood who had undergone cardiac surgery, 4 (8%) developed acute non-A, non-B hepatitis. The patients who developed hepatitis had received significantly more units of blood or blood products than the patients who had no hepatitis. The incubation period of the disease was 4-13 weeks, 3 patients were asymptomatic with peak alaminotransferase (ALT) levels of 320-497 U/1 and 1 patient was jaundiced with a peak ALT of 3,400 U/1. 1 of the patients had high ALT levels after 21 weeks of observation, while 3 patients recovered after 7-10 weeks. It is concluded that non-A, non-B posttransfusion hepatitis in Israel is a medical problem similar to that in the USA and that the clinical picture of the disease varies from a mild asymptomatic to a symptomatic and protracted course.