A-Acetylation of the insecticide Zectran does not greatly alter its toxic effects onspruce budworm, but virtually eliminates toxicity in mice. The fate of acetylated Zectran was investigated by using several radioactive labels. Mice detoxify acetyl Zectran by hydrolysis of the carbamic acid ester, producing CO2 and 4-dimethylamino-3,5-xylenol and an unknown water-soluble compound. Spruce budworm remove theacetyl group, regenerating Zectran and metabolizing part of it to 4-methylamino-3,5-xylyl-N-methyl carbamate. © 1969, American Chemical Society. All rights reserved.