The influence of maternal participation in a methadone detoxification program as compared to street drug use on intrauterine growth and neonatal morbidity was analysed in 75 newborns. -58 of 75 pregnant addicts joined the methadone program; in 17 women with successful prepartal detoxification, we found a longer course of pregnancy as well as normalized birth weight, head circumference and respiratory status of the neonates. The HIV-status showed no influence on prenatal growth. 63% of all infants developed a neonatal abstinence syndrome; this incidence was lower after maternal participation in the methadone detoxification program: 55 vs. 88%, p less than 0.05. Postnatal respiratory insufficiency occurred more frequently after methadone exposure than after heroin exposure before birth (p less than 0.05).