The effect of exposure to chronic stress on the pituitary-adrenal axis was studied in prepubertal rats. The chronic stress consisted of exposing the animals 6 days a week for 32 days to one stressor randomly chosen among several each day. Chronic stress did not alter either food intake or body weight gain. However, it was stressful for the rats, as they had increased adrenal weights. Chronically stressed rats showed normal pituitary-adrenal basal activity and normal ACTH responses to a novel, acutely applied stressor. However, this treatment resulted in higher corticosterone response to an acute stressor, as a consequence of enhanced adrenocortical response to ACTH. In addition, chronic stress induced increasing sensitivity of the adrenal to the inhibitory action of dexamethasone. Exploratory activity and defecation rate in a novel environment were not affected by the chronic stress. All these data indicate that behavioral and endocrine changes induced by chronic stress were somewhat different from those previously found in adult rats. Prepubertal rats appear to be less sensitive than adult rats to the chronic stress we used.