The invasive potential of a set of HPV-33- and HPV-33 + ras-transfected cervical keratinocytes was investigated. These cell lines were previously separated into 2 groups according to their behavior on collagen rafts. Cell lines from the first group reconstituted CINIII-like lesions, whereas cell lines from the second group reconstituted epithelia comparable to micro-invasive carcinomas. They were thus postulated to represent distinct stages of cervical carcinogenesis. The present results have shown that lines from group I, which have conserved an epithelial morphology in monolayer, (i) could not invade matrigel when tested in a modified Boyden chamber assay, (ii) produced solely gelatinase B and (iii) were unable to activate exogenous gelatinase A. On the other hand, lines from group II associated epithelial-to-mesenchymal transition (acquisition of elongated morphology, vimentin positivity) with high in vitro invasive potential and with the ability both to produce and to activate gelatinase A. These results strongly support the hypothesis that the epithelial-to-mesenchymal transition and the associated events might be implicated in the progression to the metastatic phenotype.