Three 10 micrograms of the recombinant hepatitis B vaccine, manufactured by Instituto Butantan by original technology, were administered in an adult population, mean age 30 years old, following the 0, 1 and 6 months schedule immunization. The clinical trial was considered satisfactory in terms of immunogenicity (anti-HBs titers between 17.5-29500 IU/ l, seroconversion 95.3%) and reactogenicity (no incapacitating side effects).