A comparative study was conducted on two biocatalysts, resting Rhodococcus erythropolis cells and soluble cholesterol (CL) oxidase, both catalysing CL oxidation in a cyclodextrin (CD) medium. The enzyme-mediated sterol oxidation was clearly enhanced by the dimethylated beta-cyclodextrin (Dimeb), as in the microbial oxidation. However, the microbial transformation was subject to a larger enhancement effect (enhancement factor of approx. 6) than the enzymic one (enhancement factor of approx. 2), with respect to the corresponding transformations with no CD. Rate vs substrate concentration curves of the microbial and enzymic syst ems were found to be Michaelis-Menten-like with corresponding Michaelis constant (K-m) values of approx. 0.25 and 0.5 g/l. The larger Dimeb-induced effect exerted on the microbial system was interpreted by a stronger affinity of Dimeb to the microbial cell. This CD-cell interaction was manifested through a slightly inhibited microbial growth and a limited leakage of cellular proteins and CL oxidase.