Subjects at high risks for hepatitis B virus (HBV) infection were allocated randomly (n = 591) to receive one of the two plasma-derived hepatitis B vaccines produced by the Institut Pasteur Production, Paris (HEVAC B) or the Green Cross Corporation, Osaka (GCC VAC). There are differences in the production of these two vaccines, with an added step of heat inactivation and longer formaldehyde treatment for the GCC VAC. Three doses of vaccines were given at 0, 1, and 5 months for both vaccines. Antibody to hepatitis B surfaces antigen (anti-HBs) titres were tested at 1, 3, 6, 9, 12, 18, 24 months. Antibody to hepatitis B core antigen (anti-HBc) was tested at 6 and 24 months. A fourth dose was given after 12 months to subjects who did not develop an anti-HBs titre of 10 miu/mL at month 6. Two hundred and seventy-four subjects received HEVAC B. Excluding nine subjects (3.4%) who became positive for anti-HBc, the immunogenicity was 87.2%. For the 317 subjects receiving GCC VAC, excluding 17 subjects (5.4%) who became positive for anti-HBc, the immunogenicity was 83.7% (the difference was not statistically significant). The anti-HBs titres were significantly higher in those who received HEVAC B in the 3, 6, 9, 12 and 18 months but the anti-HBs levels for GCC VAC recipients were still well above the 'protective' level of 10 miu/mL. Most hypo/non-responders did not respond to the fourth dose of vaccine. The side-effects were transient and mild, and occurred in 1.5% of subjects for both vaccines.(ABSTRACT TRUNCATED AT 250 WORDS)