Serological methods were used to detect different markers of hepatitis A and B infection in a series of 36 children aged 3.5-13 years with acute viral hepatitis, hospitalized from August 1978 to October 1978. Hepatitis A was verified serologically in 30 patients (83.3%) with the demonstration of specific IgM-anti-HAV. Hepatitis B infection was serologically confirmed in only 2 patients (5.5%). After exclusion of hepatitis A and B as well as of hepatitis due to cytomegalovirus, leptospira and Epstein-Barr virus, 3 patients (8.3) were classified to have post-transfusion non-A non-B hepatitis, and 1 patient (2.5%) showed a sporadic non-A non-B hepatitis. The finding of HBsAg in 5 of 30 patients with hepatitis A suggests that the presence of HBsAg during the acute icteric phase of viral hepatitis is not sufficient for a diagnosis of HB. The presence of HAAg in one of 30 patients with HA confirms previous studies that faecal shedding of HAV stops with the appearance of jaundice. Finally, the above results establish the value of the new radioimmunoassay technique for detection of specific IgM-anti-HAV, which appears to be the best diagnostic test for hepatitis A.