Two-photon induced polarization spectroscopy, TIPS, is demonstrated for the detection of NH3 and CO molecules. Measurements were performed in flow as well as in flame environments. The signal dependence on the laser pulse intensity and on the pump beam polarization was investigated. Two-dimensional signal intensity maps were formed from one-dimensional signal distribution measurements at different heights in flames. With a proper choice of the laser wavelength two-photon polarization spectroscopy signals from NH3 and one-photon polarization spectroscopy signals from OH could be measured simultaneously. The spectrum of the Q branch of the X1Σ-B1Σ+(0,0) band of the CO molecule at different temperatures and the dependence of the two-photon polarization signal on the number density of CO molecules in the presence of N2 and He molecules were also measured. A comparison between the TIPS and two-photon DFWM techniques for flame studies is briefly discussed.