Different strains of Culex mosquitoes (Cx. pipiens quinquefasciatus and Cx. Pipiens pallens) were immunologically-detected for organophosphate resistance with anti-esterase monoclonal antibody, and the results were compared with those detected by bioassay and biochemical microplate assay. It was found that the resistance-detection-rate detected by immunologic methods were higher than the corresponding data detected by the biochemical method, and the levels of resistance detected by sandwich-ELISA were higher than the corresponding levels detected by bioassay and the biochemical method. The thresholds for resistance in sandwich-ELISA were (at absorbence 450) > or = 0.5, and in microplate assay were (at absorbence 590) > or = 2.5 x 10(-3) mumol/min.mg protein. Dot-ELISA method was developed to meet the requirement of the field test and proved to be fast and convenient, especially in the detection of samples with higher esterase activity.