Bakers' yeast (Saccharomyces cerevisiae) has been a popular biocatalytic tool for organic chemists. More specifically, it is frequently exploited as an asymmetric reducing agent. Bakers' yeast has been found to contain many reductases, thus a library of bakers' yeast reductase chimeras has been developed and used to screen a variety of ketone substrates. This system has been used to screen the stereoselectivity of a single reductase for a given substrate by use of the pure fusion protein or used directly in whole-cells. The whole-cell method can be used as a scaleable process that affords gram quantities of optically active compounds. This process has been applied to the synthesis of several pharmaceuticals such as Prozac, Bestatin, and the Taxol side chain.