Smoking has been associated, on epidemiologic grounds, with an increased risk of cervical neoplasia. We have investigated this association, using laboratory-based methods. A 32P post-labeling assay was performed on 97 cervical biopsies to detect and measure DNA adducts (additional products formed by the covalent binding of potential chemical carcinogens to nuclear DNA). The specimens were taken from both normal cervices as well as the histologically normal regions of cervices with invasive and intraepithelial neoplasia. A detailed smoking history was obtained from each patient and correlated with an assay of cotinine level in urine. Characteristic smoking-related DNA adducts were found, and a significant difference in their levels was detected between current and non-current smokers (P = 0.017, Mann-Whitney test). There was also a highly significant trend in median adduct levels between the three tissue types (P < 0.002). We conclude that the finding of smoking-related cervical DNA damage is suggestive of a causal association between smoking and cervical neoplasia.