Thuringiensin-A, an exotoxin fromBacillus thuringiensisinhibits cell plate formation and causes bimitosis in the ensuing binucleate cells, a comparatively unfamiliar cellular response. This seems to be only chemical capable of affecting both spindle and cytokinesis. The microtubular systems are probably affected. The results suggest the potentiality of Thuringiensin-A as a tool for cell cycle analysis by marking out binucleate cells.