Three different techniques of immobilization of the enzyme butyrylcholinesterase (E.C. 3.1.1.8.) and their use in association with pH glass electrodes for the determination of certain insecticides (Carbofuran, Carbaryl, and Paraoxon) by inhibition of the enzyme, have been studied and the results obtained are compared. The immobilizations are done by cross-linking a mixture of the enzyme and human serum albumin with glutaraldehyde onto nylon nets, by fixing the enzyme onto commercially available polyamide pre-activated PALL™ membranes and by physically retaining the enzyme in a synthetic prepolymer of acrylamidemethacrylamide hydrazides which is cross-linked with glyoxal. There are no significant differences with regard to the sensitivities or the detection limits among the sensors using the different membranes. The detection limits of the insecticides tested varied from 0.2 to 10 ppm. In terms of signal reproducibility, stability, and cost, the nylon net membranes appear most promising. Membranes prepared in lots show better sensor signal reproducibility compared to those prepared individually. For the development of "disposable" biosensors, both nylon net and PALL™ membranes are very apt, since these membranes are easily mass produced at low cost and maintain their original enzyme activities even after 3 years when stored dry.