Two hundred and nineteen healthy newborns were vaccinated with the BCG vaccine, and their immunity was checked thereafter at 3, 6 and 12 months of age. We determined that 87% of tuberculin reactivity at 3 months declined to 61% at 12 months. Revaccination of nonreactive infants provided a 100% rate of reactivity. In the light of this information we propose a revision in the BCG vaccination programme in developing countries. We also found a close relationship between the tuberculin reactivity and scar formation after BCG vaccination, suggesting that a simple check of the left deltoid region for a BCG scar may give enough information about the child's immunity to tuberculosis.