Following direct infusion of morphine (0.6 to 80.0 mg/hr) to the fetal lamb for 2 to 6 hours, naloxone administration precipitated a fetal abstinence syndrome consisting of desynchronization of electrocortical activity; increased total body movements, neck tone, and eye movements; continuous rapid, deep breathing movements; immediate bradycardia associated with transient increases in systolic, diastolic, and pulse pressures; and meconium staining of the amniotic fluid. This syndrome resembles that observed in the opiate-abstinent human neonate.