The hydroxamic acid of 3'-hydroxyacetanilide (AMAP) was synthesized to test the hypothesis that different reactive metabolites of AMAP and acetaminophen account for similarities in covalent binding of the two positional isomers to hepatic proteins, but for differences in their ability to cause hepatotoxicity. N-OH-AMAP was found to be a relatively stable hydroxamic acid, but it was not detected as a metabolite of AMAP formed in vitro by mouse liver microsomes or in urine of mice administered AMAP. Therefore, metabolites other than N-OH-AMAP must be responsible for covalent binding observed with AMAP to mouse liver proteins.