Southern blot hybridisation showed that cervical cancer biopsy specimens from 31 of 47 (66%, 95% confidence interval [CI] 52-80%) patients contained HPV 16 homologous DNA sequences, with evidence of integration of viral genome into host cell chromosomes in 7. Normal ectocervical biopsies from 9 of 26 (35%, 95% CI 16-53%) control women contained HPV 16 DNA, and none showed evidence of integration. HPV 16 DNA positivity did not correlate with marital or sexual history, parity, use of oral contraceptives, or smoking habits in cases or controls, or with outcome of treatment in cases. HPV 16 DNA positivity was found less frequently with age less than 40 years old than with age greater than 40 in both cases (p less than 0.05) and controls (p less than 0.01). After age-adjustment there was no significant difference between cases and controls in frequency with which HPV 16 DNA was found. These data suggest that the association between HPV 16 and cervical neoplasia is age-mediated and that the presence of the viral genome may not always warrant intervention.