A nonhuman primate model was used to evaluate the value of the dexamethasone suppression test as an index of hypothalamic-pituitary-adrenal responsiveness to arousal. In 8 rhesus monkeys plasma cortisol was suppressed by dexamethasone in a dose-dependent fashion at doses between 0.75 and 33 microgram/kg. A replication study was performed 5 months later using a single dexamethasone dose (17 microgram/kg) known to produce maximal plasma cortisol suppression. This yielded highly correlated results (r = 0.91, p less than 0.005) suggesting that dexamethasone suppressibility may be a stable characteristic of individual animals. In 9 other animals whose arousal responses to a stressful procedure (nasogastric tube insertion) had been rated daily over a previous 3-month period, baseline plasma cortisol levels and the percent suppression of plasma cortisol by dexamethasone were evaluated. Baseline plasma cortisol levels did not significantly correlate with the degree of dexamethasone-suppression and the mean arousal ratings within animals. However, the postdexamethasone percent of baseline cortisol did correlate significantly (r = 0.75, p less than 0.025) with individual mean arousal ratings. These preliminary results suggest that assessment of the sensitivity of an individual's hypothalamic-pituitary glucocorticoid feedback system may be a better predictor than its baseline cortisol concentrations of its degree of behavioral arousal to stress.