-The impurity compositions of silicon tetrafluoride and silane prepared from it have been determined by high-resolution Fourier-transform IR spectroscopy. In the spectra of SiF 4 samples differing in purity, we have identified rovibrational bands arising from Si 2 F 6 O, SiF 3 OH, HF, SiF 3 H, SiF 2 H 2 , SiH 3 F, CH 4 , CO 2 , and CO impurities. Their detection limits lie in the range 9 × 10 -5 (CO 2 ) to 3 × 10 -3 mol % (Si 2 F 6 O). In the spectra of SiH 4 samples of different purity, we have detected CH 4 , CO 2 , SiF 3 H, SiF 2 H 2 , and SiF 4 impurities. Their detection limits lie in the range 8 × 10 -5 (CO 2 ) to 1 × 10 -3 mol % (SiF 4 ).