201 cervical punch biopsies which showed CIN lesions and were obtained between 1967 to 1977 from Falu Hospital patients, with long-term follow-up data were examined histologically and by DNA typing for human papillomavirus (HPV). We used in situ hybridization for HPV types 6, 11, 16, 18, 31 and 33 and related our findings to the behaviour of the lesion (103 regressed spontaneously and 98 progressed, some of them to invasive cervical carcinoma). There was evidence of HPV infection in 75.6% (152/201) of these lesions on histological examination, and in 53.2% (107/201) on in situ DNA hybridization. Lesions positive for HPV by both methods occurred in the younger age group (Pearson's correlation coefficient, P = 0.008). HPV 16 was found in 51/152 (33.6%) of the HPV lesions, HPV in 12.5%, and HPV 33 in 8.5% HPV 16 was highly significantly (P = 0.0001), and HPV 18 and HPV 33 were significantly (P = 0.008 and P = 0.007, respectively) associated with increasing grades of CIN. Progression to invasive carcinoma was directly (and regression inversely) correlated with the severity of CIN in the first biopsy (P = 0.005). Almost 74% (17/23) of the HPV-CIN III lesions progressed, while only 25% of the HPV-NCIN lesions (6/24) did so. The progression rate was 84.6% for HPV 33 lesions and 52.9% for HPV 16. On the other hand, progression was less common with HPV 6 (25%), and HPV 31 (30.0%). Histological grade and HPV type appear to be of value as prognostic indices.