AC 801,757 (MK-239) Is an experimental acaricide discovered by Mitsubishi Kesel Corporation which Is being co-developed by American Cyanamid Company. The now acaricide has a broad spectrum of activity on mites, with good knockdown and long residual properties. The new acaricide Is characterized by its low mammalian toxicity. In cotton, AC 801,757 at rates of 84-224 g Al/ha provided excellent control of Tetranychus urticae for 3 to 4 weeks posttreatment. No cross resistance between registered acaricides has been observed in laboratory studies.