The immunological status of BCG vaccinated and unvaccinated healthy children was evaluated to assess the efficacy of BCG. The duration of immunity conferred by the vaccine was also investigated. Of the 326 children studied, 170 (52%) had the BCG scar and only 24 (14%) showed a positive Mantoux response. Among the unvaccinated group, 14 of 156 (9%) showed a positive response. All cases had normal proportions of T and B cells in the peripheral blood. The mean values of the leukocyte migration inhibition (LMI) test with PHA were also normal. The per cent LMI values against PPD were compared in the children classified into groups based on their vaccination status and response to Mantoux test. A higher number of the vaccinated children had positive LMI values compared to those unvaccinated (p < 0.01). The LMI values of children classified into three age groups decreased significantly (p < 0.01) with increase in age. Hence, BCG seems to afford some protection in children and has to be administered at birth. Revaccination at the age of eight years, may boost the waning immunity and, may be considered in this age-group.