A 2 kb fragment containing the meso-BDH (D-AC forming) gene of Klebsiella pneumoniae IAM 1063 was cloned in Escherichia coli JM109, using the vector pUC119 to give plasmid pBUD119. E. coli carrying plasmid pBUD119 expressed meso-BDH which had the same specific activity in CFE as that expressed by strain IAM1063 grown in the presence of glucose. However, in the transformat induction of BDH expression by glucose no longer occurred. Addition of IPTG to the culture medium enhanced the production of the enzyme in JM109/pBUD119 but the stereospecificity of BDH decreased. When the transformant was cultured in LB medium containing racemic AC and 1% glucose for 35 h at 37 degrees C with shaking, only D-AC was converted to meso-BD, while L-AC remained unchanged. Thus, using these culturing conditions up to 2 g/l D-AC could be assimilated by the transformant. Recoveries of L-AC and meso-BD from the medium were 0.70 and 0.78 g/l, respectively.