The value of autotransfusion is widely recognized in the surgical community and may be of increasing importance in prevention of acquired immunodeficiency syndrome and hepatitis. The concern of possible contamination of the blood with urine, bacteria in urine or viable tumor cells has limited the wide use of intraoperative autotransfusion (IAT) in urological operation. There have been no experimental reports about protection of the blood from such contamination. To investigate separation of the blood from a contaminated mixture by using an autotransfusion machine, Haemonetic Cell Saver, a study composed of three experiments was performed. First, 200 ml of blood was mixed 200 ml of urine, and thereafter, the mixture was processed by the machine and the concentration erythrocytes were collected in a bag. Biochemical analysis of the collected erythrocyte solution (CES) was performed. Second, 200 ml of blood was mixed with 200 ml of urine that was adjusted to contain each 10(7)/ml of four bacterial strains. The bacteriological study of the CES was performed. Third, 200 ml of blood was mixed with 200 ml of urine that was adjusted to contain 10(7) cancer cells. Two cell lines, KK47 originated from human bladder cancer and ACHN originated from human renal cell carcinoma was used. The cytological study of the CES was performed. The results of these experiments were: Urine constituents were completely removed from the mixture. However, all strains of bacteria could not be separated, although the number of bacteria decreased. Cancer cells were found in the CES. In conclusion IAT should be done at urological operation in selected patients that have sterile urine and do not have tumor cells in the operation field.