In earlier experiments in our laboratory, a lectin from the Kintoki bean (Phaseolus vulgaris) was found to have not only erythrocyte agglutinating activity but also toxicities for mice and rats, including growth inhibitory activity and even lethal activity. A number of studies on legume lectins have been carried out in other laboratories as well. But relatively little attention has been paid to lectins from non-leguminous foods. In the present study, we chose Taro tuber as a source of non-leguminous lectins and prepared two types of Taro tuber lectin. One was crude lectin precipitated with ammonium sulfate from the aqueous extract and the other was pure lectin isolated as we described previously. The two were compared with regards to the antinutritional functions in mice. The daily doses were 100 mg for either intact or autoclaved crude lectin, which was a maximum amount available to give to mice in 1 ml, and 30 mg for the pure lectin which was equivalent to 100 mg of the crude lectin in hemagglutinating activity. Control mice were given 1 ml of water and the experiment was conducted for 6 days. Growth retardation was found in the mice given either lectin, but no significant difference was found in the weight increase between the control group and the autoclaved lectin group. For 3 days during the experimental period, physical activity was measured as an index of vigor of mice. The activities of the crude lectin and the pure lectin groups leveled down to 62.9 and 64.2% of that of the control group, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)