Two experiments were performed to determine the influence of stimulus specificity on differences in physiological response to stress of coronary-prone (Type A) and non-coronary-prone (Type B) individuals. In the first experiment, a reaction time task was presented to male undergraduates with and without stress relevant to the Type A behavior pattern. The physiological responses of Type A subjects were greater in the relevant stress compared to the neutral task condition, but the responses of Type B subjects were similar in the two conditions. In the second experiment, Type A and type B subjects performed a stressful task that was not theoretically relevant to the Type A behavior pattern. Physiological response elevations were found for both groups, but as predicted, there were no differences between Type A and Type B subjects. The results are discussed as support for the discriminant validity of the Type A construct and as additional evidence for the role of physiological response differences as mediators of the behavior-pattern-disease relationship.