The natural history of cervical intraepithelial neoplasia (CIN) evidenced in such pathologies a different biological behaviour due to the presence of similar morphological atypia with different potential development. To biologically characterize CIN lesions we valued by flow cytometry, the DNA content and the proliferative activity of 53 biopsies obtained by colposcopy. Aneuploid histograms were present in none of the histologically negative lesions, in 14% of the CIN I, in none CIN II, and in 40% of the CIN III. The mean value of S-phase was 2.7% in non dysplastic lesions, 5% in the CIN I, 2.5% in the CIN II and 6.1% in the CIN III. In this study the findings of aneuploid cells and the value of proliferative activities seems to be not correlated with the histological features. The clinical and instrumental follow up of the considered patients could establish the eventual prognostic significance of cytofluorimetric parameters in CIN lesions.