We succeeded expressing the streptomyces cholesterol oxidase gene (choA), a potent insecticidal protein active against boil weevil larvae, in tobacco cells. A plasmid, pBC4, containing the choA gene under the control of the 35S promoter of cauliflower mosaic virus, was introduced into tobacco cells (BY-2) using a pneumatic particle gun. Stable integration of the choA gene in the genome of the transformed callus line was confirmed by Southern hybridization analysis. Northern blot analysis revealed material corresponding in size to the choA transcript in the transformed cells. Cholesterol oxidase activity in transformed callus was about eightfold higher than that in control cell line.