A comparative cervical skin test using 1.0 mg/ml bovine purified protein derivative and 0.5 mg/ml avian purified protein derivative was evaluated as a method for detecting tuberculosis in farmed deer. A positive comparative cervical skin test reaction was defined as a bovine response with a 2 mm or greater increase in skin thickness which was greater or equal to the avian response. Estimates of the sensitivity of the comparative cervical skin test were obtained from a series of experiments conducted on 60 deer intratracheally inoculated withMycobacterium bovis. Prior tuberculin skin testing was found to suppress the skin reactivity to a subsequent comparative cervical skin test. This effect was most pronounced at short intervals of 3–7 days, but could still be measured 60 days after the previous test. When the test interval was greater than 60 days, the sensitivity of the comparative cervical skin test was 91.4%. The specificity of the comparative cervical skin test was 98.7% when 1157 deer from 17 uninfected herds with a history of nonspecific skin test reactions were examined. There was no statistical difference in the mean skin thickness increases of three groups of infected animals tested with 2 mg/ml, 0.2 mg/ml and 0.02 mg/ml of bovine purified protein derivative respectively.