The enzyme transketolase has been employed as a catalyst for asymmetric carbon-carbon bond formation in the synthesis of biologically important molecules. A number of important parameters have been addressed including substrate specificity, over-expression of the protein in suitable host systems, scale-up of the reaction and use of transketolase in multi-enzyme experiments. X-ray structural studies have been used to probe the origin of the asymmetry of the carbon-carbon bond-forming process.