A hepatitis B virus vaccine demonstration project was conducted in southwest Alaska in 1981-1982 to determine the immunogenicity and efficacy of the vaccine. A total of 1630 susceptible persons in the Alaskan Native population were vaccinated with the recommended three-dose regimen of plasma-derived hepatitis B vaccine, and 94% demonstrated antibody to hepatitis B surface antigen (anti-HBs) at levels > or = 10 mIU/mL. After 10 years of follow-up, 76% of those immunized had anti-HBs levels > or = 10 mIU. During the 10 years following the first dose of vaccine, 13 study participants developed antibody to hepatitis B core antigen (10 vaccine responders, 3 nonresponders), and none developed sustained HBs positivity or had clinical hepatitis. These data suggest that immunization with hepatitis B vaccine continues to provide high levels of protection from clinical disease for at least 10 years.