The Vero lineage, established from kidney cells of the green. African monkey, presented fibroblasts-like cells and growth in monolayers. Maintained in culture, the Vero cells presented behavioural and morphologic alterations, associated with cellular transformation. The morphological alterations were investigated using scanning and transmission electron microscopy. The study of proliferation and determination of the cellular doubling time was obtained from the growth curve. The initial population presented growth in a monolayer, while the altered cells grew in multilayers forming cellular aggregates, with flattened cells on the surface and globular cells in the inner region of the aggregate, together with extracellular matrix material. The cell surface of the altered population presented innumerable structures similar to little vesicles, microvilli and cytoplasmic prolongations. The cellular proliferation of both populations was very similar. Our results indicate that morphological and growth changes probably resulted from cellular transformation of the initial Vero cells. These transformed cells presented several characteristics associated with neoplastic growth, and can be used as a model for tumor cells studies in vitro.