In two litters of wolf cubs, individual differences in exploratory behavior, prey killing ability and social dominance were demonstrated, test scores showing a high degree of correlation as shown in an earlier study (Fox, 1972). Subjects with high, intermediate and low scores were selected for heart rate determinations monitored biotelemetrically under a test sequence designed to evaluate emotional reactivity. After these temperament and emotional-autonomic reactions had been determined, cubs were subjected to confinement and handling stress, blood samples being taken serially for plasma cortisol estimations. This treatment was repeated after ACTH injection. These findings demonstrate a marked difference in sympathetic tone and adrenal responsiveness to stress between high and low ranking cubs. High ranking cubs showed a greater sympathetic tone (higher resting EKG) and the adrenal-pituitary response to stress and ACTH treatment was of greater magnitude than in subordinates. Subjects of middle rank and with intermediate behavioral scores had a higher sympathetic tone than subordinates and under stress had a shorter latency and greater magnitude of cortisol secretion than either their higher or lower ranking peers.