The shift of the frequency of oscillation of the 00°1–10°0 rotation‐vibration band at 10.6 &mgr; of a CO2laser has been investigated as a function of total pressure, CO2partial pressure, discharge current, and cavity mode position. The measurements were made by heterodyning two passively stabilized CO2lasers, both oscillating in a single transverse mode and single frequency at thePbranch of the 00°1–10°0 rotation‐vibration band of CO2. The result yielded a 5–8 MHz/torr frequency shift toward red due to an increase in total pressure and a 500–900 kHz/mA shift toward blue due to an increase in excitation. The amount of frequency shift due to excitation was found to be independent of the location of the cavity resonance with respect to the Doppler center. The dependence on CO2partial pressure was also determined.