We determine the importance of V-V transitions in the radiative cooling by the CO2 15-μm band near the mesopause where the maximum error in cooling rate by two-level model is expected to occur. It is shown that the effect of including V-V transitions is to locally smooth the source functions for different sub-bands toward a single mean value. This effect allows the changes in cooling rate for each sub-band to partially cancel each other, so the total change in cooling rate for the whole band is not very significant. It is found that the maximum error in cooling rate around the mesopause is ~0.5 ¿K day-1. We have also examined errors in the cooling rate of the CO2 15-μm band for an equivalent two-level model suggested by Zhu (1990). The maximum error in cooling rate for the equivalent two-level model is ~1.3 ¿K day-1 around the summer mesopause. Present calculations confirm that the equivalent two-level model can be used in GCMs to calculate the CO2 15-μm band cooling rate. ¿ American Geophysical Union 1990