361 infants were seen at a total of 605 consultations at a child health centre. The aim was to study the relationship between breast-feeding practice and parental smoking at about six weeks, three months, six months and one year of age. The parents were questioned about breast-feeding, cigarette smoking and cultural origin. At the respective ages 83, 63, 45 and 15% of the infants were breast-fed. The fraction of 58 non-European mothers who breast-fed their children was not significantly lower than in our own culture. None of these mothers smoked, and their children more often had a home environment not involving exposure to tobacco. Compared with infants of non-smoking European women, a significantly lower fraction of children of non-European origin were breast-fed at six months of age, but not at six weeks and three months. Smoking was common in 40% of the mothers when the infant was six months or older. Between six weeks and three months after birth the fraction of smoking mothers increased from 28 to 37%. A significantly lower fraction of smoking mothers than of non-smoking ones breast-fed their infants between the age of three months and one year.