The metabolism of morphine was studied in seven fullterm neonates and five infants receiving a continuous infusion of morphine. All the patients had detectable plasma concentrations of morphine 3-glucuronide (M3G) and 10 had detectable concentrations of morphine 6-glucuronide (M6G). The mean plasma clearance of morphine was 20.1 ml min-1 kg-1 in neonates and 23.4 ml min-1 kg-1 in the group as a whole. The M3G/morphine ratio (7.3) was higher than that previously reported for preterm neonates (5.0) but lower than that reported for children (23.9).