Hepatitis B infection and its sequelae constitute a significant public health problem in the United States. It is estimated that 300,000 acute hepatitis B infections occur each year, with about 25% accompanied by both clinical illness and jaundice. Some infections become chronic and ultimately may cause development of liver cirrhosis or primary hepatocellular carcinoma. The risk of chronicity is especially great with infections that occur in infancy. Highly effective vaccines comprised of purified hepatitis B surface antigen (HBsAg) particles are now available for the prevention of hepatitis B infection. A first-generation vaccine utilized HBsAg derived from the plasma of infected persons; this has now been replaced by two similar vaccines that incorporate HBsAg produced by genetically engineered strains of the common bakers' yeast, Saccharomyces cerevisiae. Improved use of vaccine is needed to reduce and ultimately eliminate hepatitis B infection. Vaccination already is recommended for persons recognized to be at increased risk of exposure to virus-containing blood or other body fluids (e.g., infants born to carrier mothers, household or sexual contacts of carriers); however, mass vaccination of adolescents and infants is needed to interdict effectively a majority of all exposures to the hepatitis B virus.