Atypical mycobacteria were isolated from 240 of the 3,211 persons in Oklahoma's tuberculosis (TB) register. Fifty-one of the patients excreting atypical mycobacteria had disease caused by these organisms. Nonchromogens were the organisms in 26 (51%), photochromogens in 20 (39%), and scotochromogens in 5 (10%). A battery of mycobacterial purified protein derivative antigens (PPD-S, -Y, -G, -B, and -F) was applied to 34 patients with atypical mycobacterial disease, and to 34 patients with tuberculosis. Reactions to more than one antigen were observed in 30 (88%) of the former, and in 33 (97%) of the latter group. The largest reaction corresponded to the homologous antigen in 14 of 20 patients with nonchromogen organisms, 6 of 11 with photochromogen organisms, 1 of 3 with scotochromogen organisms, and in 28 of 34 patients with TB. Skin test reactions verified the laboratory diagnosis in the majority of cases. Multiple uniform-sized reactions were common however, and