I discuss uncertainties in the amount of mass loss and angular momentum loss during mass transfer in massive close binaries, concentrating on the first phase of mass transfer. On the basis of the reaction of the accreting star, one expects the fraction of mass lost from the binary to be a function of the orbital parameters, i.e. mass ratio and orbital period. Although spin-up of the accretor is expected to play a crucial role in limiting the amount of accretion, some binaries (e.g. φ Per) manage to have evolved in an almost conservative manner. On the other hand, common-envelope evolution is usually expected to lead to substantial mass loss, and very substantial angular momentum loss from a binary. Nevertheless there are systems that have apparently evolved through such a phase without losing much angular momentum, resulting in fairly wide current orbits
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