This study examined the relationship between moderate-level prenatal alcohol exposure, prenatal stress, and postnatal response to a challenging event in 6-month-old rhesus monkeys. Forty-one rhesus monkey (Macaca mulatta) infants were exposed prenatally to moderate level alcohol, maternal stress, or both. Offspring plasma cortisol and adrenocorticotrophic hormone (ACTH) were determined from blood samples before maternal separation and after separation. Behavioral observations were made repeatedly across separation. Moderate-level prenatal alcohol exposure was associated with significantly higher plasma ACTH response to maternal separation. Offspring exposed to prenatal alcohol, prenatal stress, and prenatal alcohol and stress showed reduced behavioral adaptation to stress compared with controls. Baseline, 2-hr, and 26-hr plasma ACTH levels were intercorrelated and predicted behavior during separation.