Skin testing with antigens from Histoplasma capsulatum, Mycobacterium tuberculosis (PPD-S), and atypical mycobacteria (PPD-B, PPD-G, PPD-Y, and PPD-platy) was carried out among six population groups in the Solomon Islands between 1968 and 1972. There was no positive reaction to histoplasmin among any of the groups, suggesting that histoplasmosis is not endemic in the Solomon Islands. There were significant numbers of tuberculin reactors among each group. Largest mean reactions to PPD-S were present among the Lau and Ulawa, in whom reactions to PPD-S were larger than those to any other antigen tested. Thus significant infection with M. tuberculosis appears to occur in these populations. This was corroborated by radiologic survey. Among the Lau, large reactions to PPD-G and PPD-Y were also elicited, raising the possibility of multiple infection. Among the Aita, Baegu, Nagovisi, and Ontong Java, PPD-G elicited the largest reactions. PPD-G produced the second largest reactions among the Lau and Ulawa. PPD-S elicited the largest or second largest reaction among 4 of the 6 groups. A notable exception was the Aita, in whom PPD-S elicited the smallest mean reaction. The Aita also had the lowest prevalence of radiologic findings consistent with tuberculosis. These observations suggest that M. tuberculosis has been introduced into the Solomon Islands from outside sources, a hypothesis which may explain the variability in prevalence of tuberculosis-like disease demonstrated by chest film among the six groups. Genetic differences may also play a role in this variability. The study also demonstrated a high prevalence of “baseline” sensitivity to the atypical mycobacteria among the Solomon Islanders. This sensitivity may confer some immunity to infection with M. tuberculosis, but this protection is far from complete.