Cutaneous reactivity to different mycobacterial antigens in patients with tuberculosis.

Mycobacterium tuberculosis and the atypical mycobacteria may give rise to similar clinical pictures. Although the etiological separation of these diseases requires special cultural techniques, the identity of the causative mycobacteria may be suggested following the simultaneous use of a series of antigens. Thus, in spite of cross-reactivity to photochromogen and to a lesser degree to scotochromogen antigens, patients with typical tuberculosis had the largest reaction to Old Tuberculin. Such simultaneous tests, when carried out with careful measurements in a standardized manner, are of diagnostic value in identifying the responsible mycobacterium.