Treatment of Kluyveromyces cells with several polycations partially neutralized their negative charge, even after washing; chitosan at 0.5 mg/ml rendered the zeta potential positive. Adhesion of the cells to various supports (glass, polycarbonate, polystyrene) was promoted by treating the cells or the support with chitosan; this confirms the importance of electrostatic interactions in the adhesion process. When the support was treated, a dense and regular monolayer of adhering cells was obtained; when the cells were treated the adhering layer was more heterogeneous due to floc formation. Cell ghosts of K. lactis were prepared by CHC13/ethanol permeabilization and glutaraldehyde treatment. Treating the ghosts with chitosan provided immobilization of 1.9 to 7.3 x 106 ghosts per cm 2 according to the support; treating the support allowed to obtain 5.5 to 5.7 × 106 ghosts per cm 2. The lactase activity of the immobilized ghosts was found to be comparable to that of ghosts in suspension, i.e. in the range of 0.9 to 2.2 U/mg dry cell weight, at 30 o C, corresponding to 0.02 to 0.14 U / c m 2 of support. A test in microreactor with a lactase solution showed that 50% of the initial activity was still found, after about 25 days of continuous operation at 30°C.