Two groups of 18 healthy adults, chosen from a risk population, were vaccinated against hepatitis B virus with French (Hevac B, Pasteur) or American (HB-VAX, MSD) vaccine; immunological and biochemical parameters (HBsAb titers, Ig, IgM-rheumatoid factor (IgM-RF) levels, autologous mixed lymphocyte reaction (AMLR), T4/T8 ratio, lymphocyte migration inhibition test (LMIT) with specific antigen and transaminase levels) were compared at preselected time intervals. The vaccines were found to be clinically safe, as documented by the absence of demonstrable side effects and changes in serum transaminase levels. The positivity of the LMIT test demonstrated an early immunization on day 45 in all subjects tested, along with a marked reduction in AMLR, independent of the vaccine used. A slightly higher, though not statistically significant, percentage of seroconversion was observed for the Pasteur vaccine. This same preparation induced a significant increase in the main Ig classes and in Ig;-RF levels on day 45. This data indicates that aspecific modification of the immune system occur to a greater extent with Hevac B, presumably for its lower degree of purification. Thus, despite the slightly lower efficacy, the HB-VAX might be the preparation of choice in subjects with immunological disturbances.