We studied the relative prophylactic efficacies of recently derived immune globulin containing antibody to hepatitis B surface antigen (anti-HBs) and hepatitis B immune globulin in 60 intimate contacts exposed to acute type B hepatitis. Forty susceptible contacts were randomly assigned to treatment with either a single intramuscular dose of immune globulin or hepatitis B immune globulin (0.06 mL/kg of body weight), following which observation was maintained over a 12-month period. Twenty additional contacts received the equivalent of twice the dose of immune globulin given to the first group, and follow-up was maintained for six months. Neither the hepatitis B virus (HBV) attack rates (11% to 19%) nor the frequency of clinical illness (0% to 4.8%) was substantially different in the three groups. When compared with average frequencies reported in the literature, significantly lower illness rates were noted for immune globulin recipients. These data indicate that currently derived immune globulin as well as hepatitis B immune globulin may confer protection from illness (le, passive-active immunity) in the setting of intimate exposure to HBV.