Despite the dangers of smoking during pregnancy having been widely publicized, few studies have actually examined the effectiveness of antismoking interventions among pregnant women in the private primary care obstetric setting. A randomized experimental study involving 24 private physicians and 109 pregnant smokers was conducted comparing the American Lung Association's Because You Love Your Baby smoking intervention (ALA) to a standard-of-care protocol (non-ALA). The non-ALA protocol was based upon the smoking interventions that study physicians said they commonly used among pregnant women. Self-reported smoking rates were obtained by questionnaire at the first prenatal visit, at 32 to 36 weeks' gestation, and at the six-week postpartum visit. By the time of the first prenatal visit, both groups reduced by half the number of cigarettes smoked. By 32 to 36 weeks, the groups decreased the daily average by an additional 2.3 (ALA) and 1.8 (non-ALA) cigarettes, a nonsignificant difference between the groups. Fifteen (28 percent) of the ALA group compared with 9 (16 percent) of the non-ALA group reported quitting at the 32- to 36-week visit (P = .10). Only 9 percent of the ALA group and 10 percent of the non-ALA were nonsmokers at the postpartum visit. Pregnancy alone is a powerful motivator for women to decrease their smoking. Although the difference between the ALA and non-ALA protocols did not attain statistical significance, the percentage of those who quit was comparable to the results obtained in other controlled trials. The ALA Because You Love Your Baby protocol should be used until more effective methods are available.