In order to determine the risk of bacterial contamination of blood during autotransfusion, blood samples were taken from the autotransfusion system of 25 consecutive total hip replacements at various stages and at different times (9 samples per patient). According to the same principle, samples were taken from the identical system after processing the postoperative drainage blood. Since the danger of contamination depends on the quality of the air which is sucked into the autotransfusion system along with the blood, we also measured the amount of bacteria in the air in two different operating rooms: Horizontal laminar air flow was provided for 20, conventional ventilation for a further 5 operations. Evaluation of airborne contamination in the operating rooms showed at most 656 cfu/m3 in the conventionally ventilated room and at most 344 cfu/m3 in the room with laminar air flow. Micrococci and peptococci were cultivated from 2 samples out of 225. The isolates were derived from 2 different patients (1 in the LAF-OR, 1 in the conventionally ventilated OR); both samples were taken from the retransfusion bag towards the completion of surgery. From these results we conclude that even in a conventionally ventilated operating room during primarily aseptic surgery intraoperative autotransfusion does not involve an increased risk of infection. This also applies to the retransfusion of processed blood from Redon drainages using the identical autotransfusion set.