We have shown previously that DNA hypomethylation is significantly associated with grade of cervical intraepithelial neoplasia (CIN; Y.I. Kim et al., Cancer, 74: 893-899, 1994). The objective of this study was to further describe this relationship and to investigate the role of folate in the observed association of DNA hypomethylation and CIN. Eighty-three patients with abnormal PAP smear results were referred to the Cervical Dysplasia Clinic at the University of Arizona for colposcopic examination and biopsy. Patients completed a short questionnaire and provided a nonfasting serum sample. DNA hypomethylation was assessed by incubating DNA extracted from biopsy samples with [3H]methyl-S-adenosylmethionine and Sss 1 methylase. Cervical tissue and serum folate concentrations were assessed using a microbiological assay. All folate levels were log transformed prior to statistical analysis. The histological distribution of the samples was: 7 adjacent normal, 30 CIN I, 18 CIN II, 13 CIN III, and 11 carcinoma in situ (CIS). The mean age of participants was 29.8 +/- 9.6 years. DNA hypomethylation was significantly different between select histological levels. Both cervical tissue folate and serum folate levels were significantly correlated to methylation level (P = 0.0211 and P = 0.0569, respectively). Smoking, hormonal contraceptive use, parity, and human papillomavirus infection were not associated with DNA hypomethylation or folate status. The current use of vitamins was significantly associated with serum folate level but not with methylation or cervical folate levels. These data extend our earlier findings that DNA hypomethylation is an early event in cervical carcinogenesis. To conclude that the folate level is significantly related to DNA hypomethylation, further investigation of DNA hypomethylation of specific genes is required.