A tunable diode laser operating in the 4.3 μm region is used to probe a conventional cw CO2 laser discharge. Vibrational populations in the 1000, 0200, 0220, and 0110 levels of CO2 are measured under lasing conditions, i.e., in the presence of intense 10.4 and 9.4 μm fields. The tunable diode laser is also used to monitor the energy transfer processes between the four levels after the passage of an intense 10.4 μm pulse. The detailed information provided by the tunable probe laser enables us to determineseparately all the vibration-vibration (V-V) and vibration-translation (V-T) rate constants of importance in the relaxation of the lower laser levels in CO2. The V-V rate constants are found to vary from a low value of 4.5×104 s−1 Torr−1 for the coupling of 0110 to 1000 to a high value of 8.0×105 s−1 Torr−1 for the coupling of 0110 to 0220.