Rate constants are reported for the vibrational deactivation of the bending modes of CD 4 and CH 4 in the temperature range 295 to 90 K for the former and 295 to 140 K for the latter. A large number of collision partners was investigated with twelve systems being studied for CD 4 relaxation and six for CH 4 . These experiments used the laser induced fluorescence technique. CD 4 was directly excited to the υ 4 level using a TEA CO 2 laser, while the υ 4 level of CH 4 was populated by collisional pumping from CD 4 . The rate constants obtained agree well with previous data for the systems where comparison with other studies is possible.