Genetically maipulated bacteria Escherichia coli K-12 recombinant PQ-37 and glucose oxidase (EC 1.1.3.4) were used for the construction of a hybrid lactose sensor because of the hyperproduction of .beta.-galactosidase (EC 3.2.1.23) by E. coli effected by a genotoxic agent. The biocatalytic layer was prepared by coimmobilization of the E. coli cells with glucose oxidase on the nylon network via glutardialdehyde and fixed to the Clark oxygen electrode. The influence of pH, temperature, and concentration of activators of .beta.-galactosidase on the sensor response was tested. Analyses of milk products were completed without any special pretreatment of the samples. The contents of lactose determined by hybrid sensor agree with conventional photometric measurements. Standard relative deviation is less than 3% for all samples. The half-life of operational stability is 30 days.