The effect of Vincaleukoblastine and colchicine on mitotic activity of bone marrow cells was studied in the Syrian hamster. Vincaleukoblastine at a dosage of 1 mg/kg. administered intraperitoneally, caused metaphase arrest of all dividing cells. Colchicine, at a dosage of 1.2 mg/kg, which caused effective metaphase arrest of dividing cells in mice, rats, and other animals, did not demonstrate stathmokinetic effect in hamsters. A single injection of 2.4 mg/kg of colchicine caused partial metaphase arrest. There was no apparent increase in the stathmokinetic effect by increasing the dose of colchicine from 2.4 to 7.2 mg/kg.