Skin-testing with paracoccidioidins (mycelial and yeast), histoplasmin, and tuberculin was done in various rural counties where recent cases of paracoccidioidomycosis had been reported. The total percentage of positive reactions to the mycelial paracoccidioidin was 9.6% and to the yeast product, 6.4%. Prevalence rates, however, varied from county to county from 6.0% to 13.0% Age, occupation, and other factors influenced such rates. Positive reactions to histoplasmin were in the range of 21.0%. The frequency distribution of the size of the reactions to the mycelial paracoccidioidin in some of the regions surveyed showed that the population was being tested with the specific antigen. In other regions, the frequency distribution revealed mainly crossreactions, possibly to H. capsulatum. The presence of a certain number of persons who reacted to paracoccidioidin but not to histoplasmin and the frequency distribution of the size of the paracoccidioidin reactions tend to show that a percentage of normal persons had acquired a benign, self-limited infection with P. brasiliensis.