AbstractHepatitis B virus markers were tested in the serum of 49 children with acute leukemia on clinical presentation and during subsequent chemotherapy. Hepatitis B surface antigenemia was observed in only six patients (12%), none of whom progressed to chronic infection. Chemotherapy had a marked suppressive effect on the production of antibodies to hepatitis B virus antigens and overt infection occurred in two children after suppression of protective immunity. Evidence of liver damage was frequently observed and was largely independent of serologic data. These results indicate that active immunization with hepatitis B vaccine may not find a clear place in this clinical setting.