We describe a stable waveguide CO2laser for spectroscopic applications. The short term spectral width is less than 10 kHz and a 10-12flicker floor is reached for the Allan variance. A study of the oscillation frequency versus resonator length demonstrates the major influence of the anomalous index of refraction of the medium. Saturation resonances with a 20 kHz peak-to-peak width have been obtained with a very good signal-to-noise ratio. A complete spectrum of SF6forP(16) at 947.74 cm-1is given as an example to illustrate the 500 MHz bandwidth of the laser.