Structural analogs of Lilly 18947 (2,4-dichloro-6-phenylphenoxyethyl diethylamine) were synthesized and tested as synergists for carbaryl, Pyrolan® (3-methyl-1-phenyl-5-pyrazolyl dimethylcarbarnate), 2,3-dimethoxyphenyl N-methylcarbamate (2,3-DPMC), and Hercules AC-5727 (N-methyl m-isopropylphenyl carbamate (IPC) on an insecticide-susceptible strain of house flies, Musca domestica L. Several, e.g. 2,4,6-trichlorophenoxyethyl diethylamine, synergize carbaryl, IPC, and 2,3-DPMC but not Pyrolan. One analog, 2,4-dichloronaphthoxyethyl diethylamine, synergizes Pyrolan, carbaryl, and 2,3-DPMC but not IPC. The results suggest at least 2 major carbamate detoxication mechanisms, one (possibly hydroxylation of N-methyl groups) active on Pyrolan, the other (possibly hydroxylation of the aromatic ring) on IPC, and both active on carbaryl and 2,3-DPMC. Some of the compounds tested are stronger carbamate synergists than sesamex.