Neurobehavioural development of a group of 35 infants of drug dependent mothers and of a reference group of 37 infants was compared. Two tailed testing showed that at the age of 3 months the infants of drug dependent mothers seemed to be more active than the reference group; at 6 months, however, no difference was found. On the infant behaviour temperament questionnaire, infants of drug dependent mothers tended to have slightly better scores for 'duration of orienting' at the age of 9 months; five other dimensions of behaviour did not differ between the groups. The Bayley scales of infant development and neurological examination according to the method of Touwen did not show any significant differences among the groups at the ages of 6 or 12 months. At 12 months infants of drug dependent mothers had slightly but not significantly worse results on electroencephalography. Studied with multidisciplinary measurements, the development of infants of drug dependent mothers does not seem to diverge particularly from the development of the reference group.