Although epidemiological studies suggest that cigarette smoking is a risk factor for cervical cancer, further evidence is required to document the biological plausibility of this relationship. This study obtained cervical mucus, using a cervical flush technique, from 50 patients in a neoplasia clinic. Nicotine was detected in the cervical mucus of all 25 smokers and cotinine in the mucus of 84% of the smokers; nicotine and cotinine levels were correlated (P < or = 0.10) with both the number of cigarettes usually smoked and the number smoked in the last 24 h. Nicotine and cotinine levels for passive smokers and nonexposed women were much lower than for women who currently smoked, with little difference found between the nonsmoking women who did and did not report passive smoke exposure. In the one woman who reported smokeless tobacco use, both nicotine and cotinine were detected at much higher levels than for other nonsmoking women. These results indicate that tobacco constituents do indeed reach the uterine cervix, suggesting that they could play a causal role in the development of cervical cancer.