Nicotine is concentrated in the cervical mucus of smokers relative to serum levels. In this experiment, the effect of nicotine on cellular proliferation of human ectocervical, endocervical, malignant, and human papillomavirus (HPV) 16 DNA-transformed cervical cell lines was studied. Ectocervical and endocervical cell lines were derived from benign hysterectomy specimens and cultured in keratinocyte growth medium. HPV 16 DNA-transformed cell lines were derived through transfection of ectocervical cells with cloned HPV 16 DNA. HPV-transformed lines and malignant cell lines established from three women with newly diagnosed cervical cancer were maintained in E-media with 5% fetal calf serum. Cells (2500-5000) were cultured in 96-well tissue culture plates with varying concentrations of nicotine (100 to 10 mg/ml) and proliferation was assessed 72 hr later with a semiautomated colorimetric assay. Experiments were performed three times and proliferation of nicotine-exposed cells was compared to unexposed cells with one-way analysis of variance. Nicotine, at 100 ng/ml to 10 micrograms/ml, significantly stimulated epithelial cell growth in two ectocervical and three HPV DNA-transformed cell lines (proliferation 118-180% of control, P < .05). Nicotine at 100 ng/ml to 10 micrograms/ml did not significantly alter proliferation of four endocervical, three malignant, and two other ectocervical cell lines. Toxic effects of nicotine (> 50% inhibition of cellular proliferation) were noted between 100 micrograms/ml and 10 mg/ml and exceed the concentrations of nicotine reported in smoker's cervical mucus. These findings demonstrate that nicotine, in physiologically attainable concentrations, does not impair and occasionally enhances the proliferation of human cervical cells in vitro. The selective mitogenic effect noted among normal ectocervical and HPV-transformed ectocervical cells may relate to epidemiologic studies showing, among smokers, an increased risk of squamous cell carcinoma, and not adenocarcinoma, of the cervix.