By using far-infrared laser spectroscopy we have studied the temperature dependence of the absorption that is due to transitions between the E¯(2E) and 2A¯(2E) levels of excited Cr3+ ions in ruby. From the temperature dependence of the linewidth we determined the inhomogeneous and the homogeneous contributions to line broadening. From the homogeneous width the lifetime of the 2A¯ level was obtained. We found that, for emperatures up to 70 K, the lifetime is due mainly to one-phonon relaxation, whereas at higher temperatures another relaxation process, probably a two-phonon Raman process, becomes strong.