The short- and long-term effects of surgical procedures and chair restraint on total plasma cortisol were assessed in the chronic rhesus monkey preparation. Three nonpregnant and six pregnant animals were sampled daily, morning and evening. Fetal plasma specimens were obtained simultaneously from the pregnant animals. In the nonpregnant rhesus monkey, a circadian rhythm is present the day following venous catheterization and chair restraint, with individual values similar to those in trained, unanesthetized animals. In the pregnant animals, a postoperative rise in cortisol is followed by a gradual decline to a plateau and a return of circadian rhythm. No consistent daily fluctuations are seen in fetal cortisol, and although correlated with maternal cortisol, the exact relationship is uncertain. The data indicate that operation, as expected, is stressful but acclimation to the chair occurs.