Mitogen- and antigen-induced interferon-γ (ifn-γ) responses of peripheral blood leucocytes from cervids were evaluated by a commercial whole-blood assay. The assay was applied to Mycobacterium bovis-infected white-tailed deer and reindeer, M bovis bcg-vaccinated white-tailed deer and elk, and unvaccinated, uninfected white-tailed deer, fallow deer, elk and reindeer. The responses of the M bovis-infected white-tailed deer to pokeweed mitogen (pwm) varied with time and between individuals. The responses of the M bovis-infected reindeer to pwm and M bovis purified protein derivative (ppd) were positively associated. Samples from tuberculosis-free captive herds in various parts of the usa were also evaluated. Four per cent of fallow deer, 20 per cent of elk, 44 per cent of white-tailed deer, and 91 per cent of reindeer had responses to pwm exceeding 0·25 Δ optical density, that is, pwm stimulation minus no stimulation. The specificity of the responses to M bovis ppd and a Mycobacterium tuberculosis complex-specific antigen resat-6:cfp-10, excluding animals not responding to pwm, ranged from 78 per cent to 100 per cent and was dependent upon the species and the positive response cut-off value. The results show that the commercial assay is valid for the detection of tb in reindeer; however, further development of the assay will be required before it is used in surveillance programmes for white-tailed deer, fallow deer, and elk.