Cytochrome P450 (CYP) 1A2 is of great interest because of its important roles in the oxidation of numerous drugs and carcinogens. Hsp70, a molecular chaperone in human, is known to assist the correct folding of unfolded proteins. To achieve high yield of recombinant human CYP1A2 in Escherichia coli, the CYP1A2 encoding gene was co-expressed with the chaperone Hsp70 under the control of an inducible tac promoter in bicistronic format. Expression level of CYP1A2 in the bicistronic construct reached up to 410 nmol (lculture)(-1) within 16 h at 37 degrees C, which is approximately 2.7-fold increase compared to the expression yield of CYP1A2 alone without Hsp70. The present over-expression system may be useful for rapid production of large amounts of active CYP1A2 in E. coli.