The ability of the yeast Saccharomyces cerevisiae to bioconvert stereo-selectively octyl-4-chloroacetoacetate (OCA) into the corresponding chiral alcohol, precursor of L-carnitin, an important physiological agent, was investigated. In a monophasic system with free cells, more than 90% of OCA (0.018 M) bioconversion have been reached after 6 h (enantiomeric excess for the R form, eeR:97%). Immobilized cells in alginate beads were less efficient in conversion of OCA than free cells. In a two-phase system with free cells, the level of reduction of OCA (0.018 M) reached 85% after 48 h. With a medium containing a higher OCA concentration (0.270 M), 41% of this product were bioconverted after the same period. On the other hand, immobilized cells did not show any significant bioconversion of OCA in two-phase reactors. The limiting factor of these reactors in the regeneration of the cofactors involved in the OCA reduction.