Pyridine solutions of copper(I) hydride plus aryl or alkyl phosphines and phosphites have been studied by freezing point depression. Cryoscopic titration curves for the most basic phosphines show a molality minimum which corresponds to the formation of R3P(CuH)2. It is proposed that association occurs via hydride bridges. 1,2-Bs(diphenylphosphino)ethane (diphos) yields a molality minimum corresponding to diphos(CuH)2. Solutions and solid samples of copper hydride-phosphine complexes do not have a high order of thermal stability, and this leads us to question the validity of a previous report on highly stable copper hydride-phosphine complexes. © 1969, American Chemical Society. All rights reserved.