Continuous infusions of MS and other opiates are widely used in the NICU as analgesics/sedatives for postsurgical pain and in neonates on mechanical ventilation. The study was designed to determine whether newborn piglets could be utilized for pharmacokinetic studies of continuous infusion MS. For this purpose, 6 spontaneously breathing conscious newborn piglets were administered a bolus of 100 μg/kg MS over 5 minutes, followed by a continuous infusion of MS at 100 μg/kg/hr for 4 hrs. Blood samples from the femoral artery and sagittal sinus vein were collected at 30 minutes post-bolus, at 1, 2, 3, & 4 hrs of infusion, and at 1 & 2 hrs post infusion for determination of plasma morphine levels by high pressure liquid chromatography. Pharmacokinetic parameters were estimated by area under the curve. Mean systemic plasma levels of morphine at 30 minutes post-bolus, at 4 hrs of infusion, and at 2 hrs post infusion were 151±45 ng/ml, 185±40 ng/ml, and 82±12 ng/ml, respectively. In the sagittal sinus vein, plasma MS levels were 133±44 ng/ml at 30 minutes post-bolus, 156±77 ng/ml at 4 hrs of infusion and 75±32 at 2 hrs post infusion. The mean clearance was 2.3 ml/kg/minute, mean volume of distribution was 2.0 L/kg, and mean elimination half-life was 8.3 hours. These data show that there was rapid equilibration of MS between the systemic and cerebrovascular circulation. The data further show that the pharmacokinetics of MS in the newborn piglet is comparable with previously reported data on human premature neonates. Therefore, we conclude that newborn piglets may be utilized as a valid animal model for further pharmacokinetic studies with MS and its effect on cerebral circulation.