Abstract: The study was intended to confirm the consistency of freeze-dried BCG vaccine production by estimating the number of viable units (NVU) as well as the induction of adequate tuberculin sensitivity mid local lesions of immunized children. The strategy followed was to evaluate the efficiency of different lots of BCG vaccine whose in vitro characteristics, especially NVU, had been previously verified, by clinical trials. For this purpose an attempt was made to investigate the influence of six selected lots of BCG vaccine with three-fold difference in the NVU on the children immunized with the same lots. The study included a total of 401 seven-year-old children. They were examined with respect to both tuberculin reactions (5 IU PPD), at two post-immunization periods - 3 months and 1 year, and local skin lesions size (at three post-immunization periods - 1 month, 3 months and 1 year). Comparing the BCG vaccine lots with NVU in the range of 3.5 x 106 to 10.6 x 106 /mg, no statistically significant differences were observed between the tuberculin reactions (P < 0.001) and the size lesions (P < 0.05). The results confirm that there is no unquestionable correlation between the NVU and the efficiency of BCG vaccine in human beings. The issue remains still disputable.