Transformation of rat embryo fibroblasts by human adenovirus type 2 (Ad2) results in the production of a series of cell lines that cover a spectrum of malignancy from nontumorigenic to highly tumorigenic in a single species. A panel of plant lectins was used to study surface characteristics of these cell lines that might correlate with tumorigenicity. Because of the complex nature of lectin-cell surface interactions, a number of parameters were determined; they included numbers and densities of lectin receptors, binding affinities, and receptor mobilities. The lectins from Lens culinaris, Lotus tetragonolobus, and Ricinus communis were found to be the most useful for differentiating among the various Ad2-transformed cell lines. In general, the more tumorigenic cell lines were characterized by high numbers of lectin receptors, high percentages of lectin-binding cells, and heterogeneous distributions of receptors from cell to cell. In contrast, the nontumorigenic and the weakly tumorigenic cell lines were characterized by low numbers of lectin receptors present on a minority of cells within each population and a more homogeneous distribution of these receptors from cell to cell. These data demonstrate that lectins can identify surface properties that appear to correlate with malignant potential in the Ad2-transformed cell lines.