Mouse T lymphocytes cultured in the presence of Vicia villosa lectin, usually considered to be non-mitogenic, proliferate and produce interleukin-2. V. villosa-induced proliferation does not correlate with the cell ability to adhere to V. villosa-coated dishes, this is evident from the fact that either V. villosa-adherent or -nonadherent cells are equally sensitive to the mitogenic effect of the lectin. Furthermore, the sugar N-acetyl-d-galactosamine, which is reported to be highly specific for V. villosa, does not reduce the lectin-induced proliferation. These data indicate that there is a difference in the carbohydrate moieties required for the adherence to V. villosa and its mitogenic effect. These results are discussed on the light of the current use of V. villosa lectin as marker for some T cell subpopulations.