The effects of variations in stress, strain, time, and temperature during thermal exposure on the tendency toward thermal instability in Ti-2Mo-2Cr-2Fe, Ti-6Al-4V, and Ti-4Al-4Mn alloys were investigated. None of the three alloys, which were vacuum annealed and given a stabilizing heat treatment before exposure, showed evidence of instability over a wide range of exposure conditions. Tests showed that a contaminated surface skin could lead to some embrittlement in Ti-2Mo-2Cr-2Fe but not in Ti-6Al-4V or Ti-4Al-4Mn. Tests on Ti-2Mo-2Cr-2Fe at four hydrogen levels resulted in the observation of embrittlement at the two higher levels—210 ppm and 330 ppm—after thermal exposure. However, tests at both slow and fast tension speeds showed that the embrittlement was due to an increase in the hydrogen-induced strain rate sensitivity and was not structural embrittlement. On the basis of these results, it can be concluded that titanium alloys are less unstable under thermal exposure than previously published data would indicate.