The more rapid rate of rise of alveolar anesthetic partial pressure in children compared with adults may be explained in part by an increasing solubility of volatile anesthetics in blood with age. To investigate this possibility, the authors measured the blood–gas partition coefficients of isoflurane, enflurane, halothane, and methoxy-flurane in four groups of fasting subjects: 10 full-term newborns (at delivery), 11 children (3–7 years old), 11 adults (20–40 years old), and 10 elderly adults (75–85 years old). The blood–gas partition coefficients were greatest in adults: isoflurane 1.46, enflurane 2.07, halothane 2.65, and methoxyflurane 16.0; and least in newborns: 1.19, 1.78, 2.14, 13.3, respectively. The blood-gas partition coefficients in children (1.28, 1.78, 2.39, 15.0, respectively), which were intermediate between those in newborns (P< 0.005) and those in adults (P< 0.005), were not significantly different from those in elderly adults (1.29, 1.79, 2.41, 15.0, respectively). The blood–gas partition coefficients of both isoflurane and enflurane correlated directly with the serum albumin and triglyceride concentrations; that of halothane correlated directly with the serum cholesterol, albumin, triglyceride, and globulin concentrations; and that of methoxyflurane correlated directly with the serum cholesterol, albumin, and globulin concentrations. The authors conclude that 1) age significantly affects blood–gas partition coefficients, and 2) the lower blood–gas partition coefficients in children explain in part the more rapid rise of alveolar anesthetic partial pressure in this age group.