After obtaining institutional review board approval, and written parental informed consent, we will recruit 45 children for Phase I aged 2-6 years undergoing elective surgery. A perceived ethnicity questionnaire will also be administered. Subjects recruited for Phase I will be block assigned to one of the three doses of morphine. In Phase I, sampling will be done for 4 hrs to determine the key pharmacokinetic parameters including Tmax, Cmax and AUC. Monitoring will occur throughout and analgesic efficacy and adverse effects will be measured post-operatively. All subjects will receive 24 hr telephone follow up for analgesic efficacy and adverse drug effects.