Acetoxime was tested for carcinogenicity by chronic administration in the drinking water to male and female outbred MRC-Wistar rats. The dose of 1.0 g/liter was administered 5 days/week for 18 months (total dose, 6.2--7.0 g/rat). The test compound induced benign hepatocellular adenomas in 80% of the males but did not produce tumors in the females. This is the first report that oximes, which are fairly widely used in industry, are tumorigenic.