Acid-fast microorganisms were identified from the tuberculous lesions of a male cynomolgus monkey (Macaca fascicularis). Twenty-two other cynomolgus monkeys housed in the same room were presumed exposed to tuberculosis (Mycobacterium spp.). In addition to standard intradermal (ID) tuberculin testing, clinicians attempted to evaluate the immune status of these monkeys in order to identify animals exhibiting false negative (anergy) ID tuberculin tests. Twenty-one of the potentially exposed monkeys were immunized with tetanus toxoid (TT). Tetanus antitoxin (TAT) titers were measured before and after immunization. The delayed cutaneous hypersensitivity (DCH) reaction to TT was evaluated using a commercially available human test panel. Some animals did not exhibit a DCH reaction to TT. At necropsy 1 of the 21 animals exhibited tuberculous lesions, and acid-fast microorganisms were identified on direct smears of lymphatic tissue of a second animal. Although reported to be of value in assessing the cellular immune status of rhesus monkeys (Macaca mulatta), the delayed cutaneous hypersensitivity response to tetanus toxoid was not helpful during this outbreak in identifying cynomolgus monkeys infected with M. tuberculosis, or in interpreting suspect ID tuberculin tests.