Klebsiella oxytoca (NRRL‐B199), although able to produce 2, 3‐butanediol from glucose, converted lactose mainly into acetic acid. By addition of a preparation of lactase (β‐galactosidase, EC 3.2.1.23), the fermentation of lactose in a stirred vessel was three‐times faster and resulted in a high concentration of 2, 3‐butanediol. The lactase confined in dead cells of Kluyveromyces lactis (CBS 683) was prepared by permeabilization with solvents and fixation with glutaraldehyde. The cells were coimmobilized by adhesion to glass wool after treatment of the latter with chitosan, which ensured cell‐support electrostatic attraction. The cell loading (dry weight) was ca. 9 gL⁻¹ for the yeast and ca. 2 gL⁻¹ for the bacteria. In the presence of culture medium, the adhesion of both cells was stable and the bacteria tended to form biofilms. The stability of the coimmobilized cells was demonstrated by the continous conversion of lactose into 2, 3‐butanediol at 30oC during 25 days. The coimmobilization system gave output concentrations (14 gL⁻¹) and rate of production (1 gL⁻¹ h⁻¹) of 2, 3‐butanediol from lactose, similar to those obtained in the literature with immobilized cells and glucose. Compared to the literature data on direct conversion of lactose using pure cultures, the present results showed higher butanediol concentrations and 10 to 100 times higher rates of production.