Female macaques were tested under two different psychologically stressful situations in which plasma ACTH and glucocorticoid concentrations were measured. In the first, animals were operantly trained to enter a small transport cage over a four-week period, and plasma ACTH and glucocorticoids were measured in response to brief confinement in the cage before and after training. ACTH values were significantly lower in the pre-test (stress) condition when compared to those for the post-test, whereas the opposite result was found for glucocorticoid values. In the second experiment, blood samples were collected before and one hour after exposure to more acute and severe stress (restraint, venipuncture, handcapture, transport). Both ACTH and glucocorticoid values were significantly elevated from baseline at the post-test sample. The differential relationship between the two hormones among the two experiments was likely the result of the specific timing and magnitude of the stress imposed by each test situation.