A tunable diode laser (TDL) operating in the 2150–2350 cm−1 wavenumber region is used to probe a conventional cw CO2 laser discharge. Absorption lines in more than 25 different vibrational bands are observed, enabling us to determine absolute vibrational populations inall levels of concern to the dynamics of the 10 μm CO2 laser. Levels in thev3 mode of CO2 as high as 00°9 are monitored, and it is found that anharmonic effects play a significant role in the populations of such levels. Thev1 andv2 mode populations are also investigated in detail, and it is found that these modes are strongly coupled and maintain a common vibrational temperature under all discharge conditions. The use of a TDL is shown to be a powerful technique for investigating the dynamics of infrared molecular lasers.