The motion of the circumstellar gas in close binary systems is studied for systems where the secondary is believed to be a black hole. We treat mass loss from the primary star by overflow through the inner Lagrangian point and by a stellar wind efflux. The flow in these models is discussed and compared with the available observational material. It is, however, found that more comprehensive observations must be made before the final choice can be made between these two means of mass exchange.

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... possibility, that streams ejected from a circumstellar disk around the black hole reach the far side of the primary star, is briefly discussed.