The relationship between the quantity of methadone ingested by the pregnant mother, the quantity of methadone in maternal and neonatal body fluids, and the subsequent neonatal withdrawal course was studied. The severity of the neonatal withdrawal syndrome was found to be related to the total dose of methadone ingested by the mother during the last 12 weeks of pregnancy (p less than 0.02), the maternal dose of methadone at delivery (p less than 0.01), and the intrapartum serum methadone levels (p less than 0.01). The cord blood levels of methadone were consistently lower than the maternal serum levels. Amniotic fluid methadone levels were not constantly related to maternal or neonatal serum methadone levels. Concentrations of methadone 10 to 60 times greater than that of cord blood were found in neonatal urine.