A capacitive chemical sensor for fenvalerate is reported. By using ac impedance measurements the sensor has been based on the decrease in capacitance caused by the analyte used as the template in the formulation of an electropolymerized molecularly imprinted polymer as receptor layer. Improvement of the insulating properties of the sensor was investigated in detail. The capacitive sensor was prepared by a deposition of a self-assembled monolayer of 2-mercaptobenzimidazole (2-MBI) before electropolymerization of 2-MBI and subsequent treatment with n-dodecanethiol to eliminate pinholes and defects in the polymerized 2-MBI film. From the calibration curve concentrations of fenvalerate up to 9 microg mL(-1) could be detected with a linear determination range up to 5 microg mL(-1) and a detection limit of 0.36 microg mL(-1). No significant interference was observed from common pyrethroid insecticides.