Biocatalytic direct monohydroxylation of anilides has been achieved on preparative scale using mutant cytochrome P450_BM3 enzymes. Representative mono- and disubstituted N-trifluoromethanesulfonyl anilides are shown to be converted in most cases to the corresponding 4-hydroxy derivatives, with substituent hydroxylation also occurring in two cases. By mutation variation, it is possible to achieve selective hydroxylation of either ring- or side-chain sites.