Health authorities have estimated a low immunity level against diphtheria, tetanus, poliomyelitis, measles, mumps and rubella among adults in Lithuania due to less than optimal vaccine quality. The aim of this study was to evaluate the level of immunity by blood sampling 100 young women, 50 young men and 50 middle-aged men and from the immunization history by questionnaire. Lack of protection against diphtheria was found in 0%, 2% and 46% of the young women, young men and middle-aged men respectively. The corresponding data for tetanus were 0%, 0% and 10%. It was found that 85% of the women had antibodies to all 3 types of polioviruses vs. 80% of the young men and 56% of the middle-aged men. A sub-protective antibody level against measles was found in 12% of the women, 22% of the young men, but in none of the middle-aged men. A protective titre of rubella antibodies was found among 94% of the young, pregnant women. It can be concluded that the level of immunity in Lithuania is comparable to that in Western Europe for the same age groups and that the launching of adult vaccination programs in Eastern Europe should be preceded by sero-epidemiological studies.