Intraperitoneal injns. of urethane (NH2COOC2H5)[long dash]1 ml. of a 10% aqueous soln. per 100 g. of body wt.[long dash]almost wholly does away with all stages of mitosis for a period of 8-12 hrs., judging from counts of mitotic figures in sections of the corneal epithelium from rats and mice. Lung tumors of adenomatous type appeared in 75 of 86 animals treated with urethane. The connection between the interference of this drug with mitosis and its causation of lung tumors is not evident.