We tested the hypotheses that in early pregnancy smokers have lower urinary cotinine levels than nonpregnant smokers, and that pregnant nonsmokers exposed to passive smoke have higher cotinine levels than nonsmokers not exposed to passive smoke. This was a prospective, quantitative, comparative study of the urinary cotinine levels and smoking characteristics of pregnant and nonpregnant females. A urine specimen was collected from each subject and the cotinine/creatinine level determined using radio-immunoassay. A questionnaire regarding smoking status, health issues, and demographic variables was administered to each subject. There was no difference in cotinine level between pregnant smokers and control smokers. Pregnant nonsmokers with passive smoke exposure had higher cotinine levels than the same group not passively exposed. Confidence in ability to stop smoking was associated with lower numbers of cigarettes consumed, but was not reflected by lower cotinine levels. These data suggest that if the mother smokes, the fetus is exposed from conception to levels of nicotine which are as high as those in adult female smokers who are not pregnant. The level of fetal exposure to nicotine during early gestation is independent of intention to alter smoking behaviour. Women should be targeted for antismoking public health messages before conception.