For the purpose of establishing the maximum cutoff point defining a positive tuberculin reaction in Cantabria, a study was made of a total of 1,814 school-age children, 7 and 14 years of age, selected at random from the school-age children in that region. 2 U of PPD RT-23 were used. It was observed that 26.8% of these children had a scar from having been vaccinated with BCG. The graph of induration frequencies is bimodal for both age groups and for those vaccinated and those not having been vaccinated. In the 5-9 mm. range, 69 (71%) of those studied had a scar, and 25 (26%) did not (p less than 0.001). In our region, a different cutoff point must be used for the purpose of this test: 5 mm. for screening and 10 mm. for estimating the prevalence of infection.