The product (S)-p-chlorodiphenylmethanol is obtained through stereoselective reduction of p-chlorobenzophenone using Debaryomyces marama cells, immobilized on Raschig rings. This process involved continuous fermentations in bioreactors for a period of 10 days. The conversion was 86% with a volumetric productivity of 0.248 litre(-1) d(-1). Comparative experiments with D. marama cells, incorporated in alginate, k-carrageenan or agar-agar gels were also performed. These results demonstrated superiority of the immobilization on ceramic carriers compared to other methods. Passive immobilization of D. marama cells on ceramic carriers has many advantages in comparison with gel-incorporation of the cells. For example, during a long bioreactor run, only a limited amount of cells could remain incorporated within the gel. Therefore immobilized cell preparations will be a convenient methodology in the production of optically active compounds such as pharmaceutical drugs.