p-Nitrophenyl-, alpha-naphthyl-, and beta-naphthyl-(1,R)-cis-3-(2,2-dibromovinyl)2,2-dimethyl cyclopropane carboxylates are proposed as pyrethroid-like substrates for the detection of pyrethroid esterases (PyEs). 2. The substrates have been used in a spectrophotometric assay of PyEs and in a staining method to locate PyEs on polyacrylamide electrophoresis.