 The primary aim of this double-blind, placebo controlled, randomized, multi-site study is to demonstrate improved pulmonary function testing at 3 months of age, in infants delivered to smoking mothers who are randomized to 500 mgday of supplemental vitamin C versus placebo at less than or equal to 22 weeks of pregnancy. We will recruit 278 smoking pregnant women into the study. Patients will meet with research personnel at each prenatal visit and smoking cessation will be actively encouraged. Patients will be monitored with a set of serial biomarkers to assess smoking and medication compliance, including urine cotinine levels, smoking questionnaires, pill counts and fasting plasma ascorbic acid levels. Pulmonary function tests will be done at 3 months of age and will measure forced expiratory flows. The infants will also be followed through one year of age with monthly validated respiratory questionnaires and a follow-up pulmonary function test at 12 months of age. Success of this study is supported by strong pilot data showing statistically significant improvements at about 48 hours of age in pulmonary function tests in infants born to smoking mothers who received vitamin C versus placebo, and preliminary data showing a lower incidence of wheezing at 12 months of age in these infants. Key genetic polymorphisms shown to increase sensitivity to in-utero smoke exposure will also be measured. The success of this study is also supported by animal models showing the effectiveness of vitamin C to preserve pulmonary function and genetic and epidemiologic studies linking the effects of smoking during pregnancy to oxidant mechanisms. The secondary aims of the study include: 1 to demonstrate a decreased incidence of wheezing through 12 months of age in infants delivered to smoking mothers who are randomized to 500mgday of supplemental vitamin C versus placebo during pregnancy; 2 to demonstrate improved pulmonary function tests at 12 months of age in these infants. 