A method for stabilizing a cw CO2laser using a molecular beam absorption signal as an external reference is described. The laser may be stabilized at line center or at any offset within the Doppler width by Stark tuning the absorption frequency. A time‐domain fractional frequency stability of &sgr;(&tgr;)=2.03×10−10&tgr;−1.3was measured with another CO2laser independently stabilized on the Lamb dip of the 4.3‐&mgr;m fluorescence.