The present report summarizes our current observations on the natural history of cervical HPV (Human papillomavirus) infections, based on data from 418 women prospectively followed-up in our clinic for a mean of 20 +/- 15 (M +/- SD) months. On each attendance at the clinic (at 6-month intervals), the patients are subjected to colposcopy accompanied by PAP smears and/or punch biopsy, both being analysed for the cytopathic changes of HPV, and for concomitant CIN (cervical intraepithelial neoplasia). In the biopsies, the expression of HPV structural proteins was assessed using an indirect immunoperoxidase (IP-PAP) technique. HPV typing was accomplished by spot hybridization with the DNA probes for HPV 6, 11, 16 and 18. During the follow-up, 24% of the HPV lesions regressed, 55% remained persistent, and 21% progressed, 10.6% having been coned due to progression into CIS. The clinical progression was significantly associated with the grade of HPV-associated CIN. On DNA hybridization, HPV 6 was found in 8%, HPV 11 in 36%, HPV 16 in 11% and HPV 18 in 8% of the 103 lesions typed for HPV DNA so far. HPV-CIN lesions were more frequently than HPV-NCIN associated with HPV 16 and HPV 18, as was the expression of HPV structural proteins. The progression rate was highest (45.5%) in HPV 16 lesions, followed by that (27.3%) in HPV 18 lesions, as contrasted to 0% and 13.3% for HPV 6 and 11, respectively. The natural history of cervical HPV lesions seems to be identical with that of classical CIN lesions.(ABSTRACT TRUNCATED AT 250 WORDS)