BACKGROUND: The bcl-2 proto-oncogene codes for a protein which appears to block apoptosis. In our study, we examined bcl-2 protein expression in cervical squamous metaplasia, cervical intraepithelial neoplasia (CIN) and microinvasive squamous carcinoma with the aim of identifying a relationship between bcl-2 protein expression and neoplastic development and progression. MATERIALS AND METHODS: Cervical bioptic samples were obtained from 86 white women, selected consecutively from our Colposcopic Service from January 1993 to June 1994, because of abnormal pap- smear suspicious for cervical dysplasia and/or human papilloma virus (HPV) infection. Upon histologic evaluation, 41 women had CIN, 23 cervical condyloma, and 22 squamous metaplasia. Ten patients with microinvasive squamous carcinoma, matched for age and demographic characteristics, were selected from our series of invasive cervical carcinomas and immunohistochemically analyzed. The expression of primary tumor bcl-2 protein was immunohistochemically evaluated by antihuman bcl-2 monoclonal antibody (diluted 1:100, Dako, Copenhagen, Denmark) on formalin-fixed paraffin-embedded tissue. Positive staining was expressed as a percentage of positive cells per 1000 counted dysplastic cells for each case. RESULTS: Bcl-2 immunostaining was found in all the 22 squamous metaplasias, limited to the basal layer. Nineteen of the 41 CINs (46%) were bcl-2 immunoreactive, and 2 of the 10 microinvasive carcinomas (20%). By analysing CIN lesions, the bcl-2 protein showed a striking increase in the rate of positivity with increasing severity of CIN; the bcl-2 protein expression in CINs III was significantly higher than for CINs I, CINs II or microinvasive carcinomas (P = 0.03, P = 0.02, and P = 0.03 respectively). No relationship was observed between bcl-2 immunostaining and HPV infection. bcl-2 protein expression was not useful for predicting CIN I and II evolution, although the rate of persistence/progression was higher in bcl-2 positive dysplasias (7 of 9 cases, 78%) than in negative ones (13 of 21 cases, 62%) (p = 0.88). CONCLUSIONS: Based on these results, it seems possible that the increase in bcl-2 expression in higher grade of CINs implies an increasing protection against programmed cell death, but also the induction of genetic instability in dysplastic epithelial cells and a greater capacity to evolve into invasive carcinoma.