With the aim of evaluating the immune response obtained after the administration of the three standard doses of Hepatitis B vaccine obtained by recombinant DNA techniques (Engerix B) and the factors that may have an influence in it, we have studied 537 subjects belonging to different risk groups. The ratio of non-responders to the vaccine has been. We have found significant differences (p less than 0.001) when comparing the mean titers obtained amongst the groups of studied. We have observed a higher percentage amongst the non-responders in men, although there are not statistically significant differences between sexes. We compare the results obtained with those published by other groups.