Healthy infants, children, and adolescents presenting for routine care or elective surgery have a single blood sample obtained. Blood is used for complete blood count, peripheral blood mononuclear cell flow analysis for surface markers, and plasma and cell storage. Demographic information including age, sex, race, and ethnicity is obtained at the time of the blood draw. The reason for the patient's visit is also documented. No study drugs are administered or supplied as part of this study. Statistical analysis is used to estimate the median distribution of each CD4 and CD8 subset.