This study investigated the effects of varying durations of exercise training on heat shock proteins 72 and 73 (HSP72/73) induction in the rat adrenal gland. Female Sprague-Dawley rats (120 days old) were assigned to either a sedentary control group (C) or one of the three endurance exercise training groups. Trained animals ran on a treadmill at approximate to 75% VO2max for 10 weeks (4-5 days week(-1)) at one of the three different exercise durations (30 min day(-1) = T30, 60 min day(-1) = T60, or 90 min day(-1) = T90). All durations of exercise training resulted in an increase in the HSP72 levels (P < 0.0001). The magnitude of the training-induced elevation in the HSP72 levels in the adrenal gland increased as a function of the training duration (approximate to 60-fold increase in T90; approximate to 40-fold increase in T60; and approximate to 15-fold increase in T30). Longer exercise durations (> 60 min day(-1)), also resulted in small but significant increase in HSP73 level (approximate to 1.2-fold increase in both T60 and T90; P < 0.05). These results demonstrate that the physiological stress created by chronic treadmill running can induce both HSP72 and HSP73 in rat adrenal gland. Increased levels of adrenal HSP72/73 expression during rigorous exercise, may be one of the adaptive mechanisms of the adrenals to cope with an increased dose of stress.