The existence of Wolf-Rayet binary systems containing a collapsed companion is predicted on evolutionary grounds. However, because of the absence of strong X-ray emission and the difficulty in obtaining consistent periodicities from the observed variations, none of the “classical” WR stars has been shown to be a WR+cc system. A discussion is presented of the line-profile variations which are predicted to occur on orbital timescales due to the interaction of the WR wind with the cc. We note the importance of numerical simulations of the flow structure of the WR wind in the vicinity of a collapsed companion for deriving diagnostic tools for the presence of a cc in a WR system.
