Studies on the interactions of benzylic alcohols, aldehydes, and carboxylic acids with homogeneous preparations of aryl sulfotransferase (AST) IV have yielded information about the nature of the active site of the enzyme. Lipophilicity and stereochemical configuration of benzylic alcohols are key factors in determining their interaction with the active site of AST IV. Furthermore, aldehydes and carboxylic acids corresponding to the subsequent oxidation states derived from benzylic alcohols are inhibitors of the enzyme. Additional investigations on the catalytic specificity of AST IV indicate that both primary and secondary N-hydroxy arylamines can serve as substrates for the enzyme. These results with benzylic alcohols, aldehydes, carboxylic acids, and N-hydroxy arylamines have yielded insight into some of the parameters important in recognition of substrates and inhibitors by the active site of the enzyme and should be useful both in understanding in vivo metabolic interactions and in designing appropriate new inhibitors to use as selective probes for the role of sulfation in metabolism of specific xenobiotics.