A survey of the smoking habits of 3,025 couples, whose infants were receiving medical examinations, was conducted before and after pregnancy to determine the effect of smoking patterns of the parents on the newborn infant. Of the husbands 55.2% were smoking before pregnancy; 53.4% during pregnancy; and 51.8% after delivery. During pregnancy proportion of smokers decreased by only 1.8%. The percentages for wives, on the other hand, were 13.9%, 4.4%, and 5.3% respectively showing a reduction of 9.5% during pregnancy. Young couples, under 24 years of age, those with low educational backgrounds, and self-employed husbands showed the highest proportion of smokers. Examination of the relation between parents' smoking habits and their effect on the newborn infants, showed no difference in weeks of gestation nor in height. However, the infants of smoking parents were on the average 99.6 grams lighter at birth (p less than 0.02) and the rate of SFD was higher (p less than 0.05). The relative risk for SFD appearance was 1.21 with a smoking father, and 1.39 with both parents smoking. Husbands who decreased or stopped smoking during the pregnancy were largely in the 30 to 34 year old category, university graduates, and those whose wife was having their first baby. A remarkable decrease was observed in the average weight at birth of infants with a mother smoking 6 cigarettes a day or with father smoking 20 cigarettes a day compared to non-smoking parents, especially in the case of female infants.(ABSTRACT TRUNCATED AT 250 WORDS)