The plea by Cramblett, et al. (Pediatrics, 38:381, 1966) for assistance in obtaining mycobacterial antigens deserves strong support. From their and other data it appears that infection with atypical mycobacteria is not a rare phenomenon. At present, those of us in practice have no way of diagnosing most of these patients. Young children with a positive tuberculin test (PPD-S) are, therefore, usually treated prophylactically with isoniazid, even in the absence of other findings. If antigens for the atypical mycobacteria were available, specific diagnoses could be made.