A group of 106 adult Panamanian men were skin tested with a standard human tuberculin (RT 23) and three sensitins prepared from atypical mycobacteria. Two of the sensitins (prepared from Mycobacterium kansasii and Battey organism) are commonly used to detect atypical mycobacterial infections. The third (prepared from M. xenopi) had not been used in Panama previously. Skin sensitivity proved to be significantly higher to the M. xenopi sensitin than to the others. The known epidemiology of M. xenopi is briefly reviewed.