Klebsiella pneumoniae IAM 1063 forms 2,3-butanediol consisting of a mixture of the meso- and L-isomers from glucose. A gene fragment including genes coding for three enzymes (ALS, ALDC, and meso-BDH (D-AC forming)) involved in the formation of meso-BD of K. pneumoniae IAM 1063 was cloned in Escherichia coli JM109 after its insertion into pUC118. The resulting E. coli JM109/pBDO118 was cultured in LB medium containing glucose and formed only a meso-isomer with no contamination of the L-form. Various culture conditions for the production of meso-BD were tested. The highest meso-BD yield of 27% (w/w, 10.7 g/l against initially added glucose was obtained in a LB culture shaken for 24 h at 30 degrees C in the presence of 4% glucose. However, re-conversion of meso-BD to AC occurred with time. The highest productivity of meso-BD was 17.7 g/l, which was obtained using an initial glucose concentration of 10%.