Levels of antibody to hepatitis B surface antigen (anti-HBs) were measured in thirty young healthy volunteers given 20 ug dose of Korean Green Cross plasma derived hepatitis B vaccine (Hepavax B ) monthly at 0, 1, 2 month schedules. Blood samples were removed monthly for three months after injection of 1st dose vaccine and tested for anti-HBs by radioimmunoassay. Antibody (anti-HBs) conversion rate was elevated up to 93% one month after third dose injections in these volunteers and geometrical mean antibody titers expressed as ratio units were 37.3 RU at this period (>10 RU: 76%). There was no sigificant difference in immunogenecity between the 2 month and the recommended 6 month schdeules, the shorter schedule is likely to be more convenient in certain situation, such as mass hepatitis B vaccination.