A prospective study of 196 drug-addicted mothers and their infants was conducted to determine the maternal, fetal, or environmental factors that may affect the severity of narcotic withdrawal in the infants. The severity of neonatal withdrawal did not correlate with the infant's gestational age, sex, race, or Apgar score, not to maternal age, parity, duration of heroin intake, or the level of morphine measured in the infant's urine or blood. Reduction in the amount of illumination and noise in a study nursery also did not lower the incidence of severe withdrawal in the infants. There was, however, significant correlation between the severity of withdrawal in the infant and the maternal methadone dose (p less than 0.025). It is therefore recommended that mothers on methadone treatment be put on a low dose of the drug (less than 20 mg/day) as soon as is safely possible to prevent serious withdrawal in her infant.