When a vaccine in three different concentrations (non-diluted, half-strength and one-third strength) was used on a study population of 159 students, six weeks after the vaccination only the vaccine at one-third strength showed small vaccination lesions in comparison with those of the other two concentrations. There is no evidence of any significant difference between them with respect to the positive reaction to the tuberculin testing. After one year, the number of subjects with a positive vaccination scar is drastically reduced in the case of the vaccine at one-third strength. As regards the tuberculin reaction, even if the difference in the number of positive values is not significant, the reaction size for the one-third and one-half strength dose diminishes significantly with respect to that observed at six weeks.