According to the investigations carried out it was found that infections caused by myobacteria are widely distributed in the subtropical zone and in areas where sanitary facilities are scarce and a dense population exists. It was decided to verify the basis of this hypothesis with an analysis of details collected with the aid of the Mantoux test of tuberculine PPD-S, PPD-Y, PPD-B, and PPD-G antigens in 1000 children from 3 to 14 years in Peru. The authors made sure that all children who were classified had not been vaccinated or had received vaccination over two years ago. Reading should be carried out after 72 hr by well trained staff making sure of proper asepsis conditions for each antigen. Only those cases in whom readings of 10 mm or more were obtained were considered for the index rate of infection and prevalence of reactors. It was verified that: 363 children reacted to the PPD-S (with 10 mm or more), giving a 36.3% infection index (19.5% girls and 16.8% boys); 262 children reacted to the PPD-Y, giving a 26.2% infection index (13.3% girls); 161 children reacted to the PPD-B, giving a 16.1% infection index (8.2% of which were girls); and 192 children reacted to PPD-G, giving a 19.2% index and a 9.4% share for girls.