BACKGROUND While homeostatic mechanisms are generally believed to become less efficient in the aging organism, evidence for changes in hypothalamic-pituitary-adrenal function is inconclusive. Previous studies report higher, lower, or unchanged basal cortisol levels in human aging. Delayed recovery of glucocorticoids to baseline following stress exposure has been observed in aging rats, but the generalizability of these findings to humans remains unclear. METHODS Salivary-free cortisol was measured at home and in response to a laboratory speech task in 56 healthy men and women in three age groups (range 43-86 yr). RESULTS Higher basal cortisol levels were observed in older age groups. Gender, recent life stress, and current distress showed no relationship to basal levels. The magnitude of cortisol responses to the speech task differed by age, with the smallest responses in the oldest group. This pattern was robust in men, with the youngest subjects (40-59 yr) showing both the largest and the most prolonged responses. While women > 70 yr were least likely to show any response, other analyses failed to show age effects on reactivity in women, perhaps because anticipatory baseline elevations limited subsequent cortisol response. CONCLUSIONS Results indicate moderate increases in basal cortisol levels, but do not support the hypothesis that cortisol responses to a stressor increase in magnitude or duration during normal human aging. Gender differences in stress reactivity warrant further investigation.