The somatic cell changes which characterise malignancy evolution in human cervical preneoplastic and neoplastic lesions have been assessed on histological sections by means of a computerised image analyser. Many features have been simultaneously measured on each cell of the lesions studied, and the following results have been obtained: Some features, mainly kinetic, show continuously increasing values which express changes correlated to the increasing malignancy; other features, especially related to nuclear atypia, cellular heterogeneity and the degree of aneuploidy, have values dropping at the level of early stromal infiltration, which can be morphometrically characterised as composed of relatively homogeneous phenotypes; these features seem to express the degree of genetic instability and relate to the evolutionary somatic cell changes; tumour progression evolves through sequential discontinuous steps, each of them characterised by specific phenotypical features of the neoplastic cell population; the neoplastic cells in the foci of early stromal infiltration and vascular invasion, phenotypically more homogeneous than the parent cell populations of carcinoma in situ and infiltrating carcinoma, seem to possess a greater genetic stability.