We report on the application of polarization spectroscopy in the mid-infrared spectral region for the detection of methane by probing its asymmetric ro-vibrational transitions. Tunable infrared laser radiation, near 3.4 μm, was obtained from difference-frequency generation in a LiNbO 3 crystal. Infrared polarization spectroscopy (IRPS) spectra of the P, Q and R branches of the ν 3 band, recorded with both linearly and circularly polarized pump beams, are presented. The experiments were performed in an atmospheric pressure gas jet with methane diluted with Ar. An IRPS spectrum with signal-to-noise ratio better than 10 4 was observed. The dependence of the IRPS signal intensity on the methane mole fraction and on the pumping laser power density was investigated. ; The original publication can be found at www.springerlink.com