Such a process as autotransfusion has been known for a very long time now. This method means that the blood taken from a patient is given back to that patient later. At the early times of blood transfusion that was the only way to perform it. At the beginning of the 19th century, there was no knowledge about blood types so that blood could not be taken from one patient and given to another. Therefore, in surgery doctors used different methods of autotransfusion. And it wasn't until much later that a blood group was discovered. That led to a development of blood banks and people started to use blood of other patients for transfusion. But a great number of problems arose. Unlike the regular technique of transfusion, blood bank autotransfusion gives no reactions and excludes the risk of transmitting infections. So, in the following years a technique of autotransfusion was also developed and today it is still in wide use. Autotransfusion is applied today as a preoperative donation (a patient's own blood that was taken before the actual surgery operation is transfused during the surgery) to collect the lost blood in operations and return some of it to the patient. The physical principles of autotransfusion systems allow for a fast and easy performance. With the use of principles of autotransfusion systems it is also possible to collect lost (drainage) blood, purify it and return to a patient or use it in further retransfusion. Such systems are called direct autotransfusion systems and are in wide use in modern medical practice. But are they safe enough and able to produce high-quality blood? According to physical principles of autotransfusion systems the quality of blood produced in a purifying process is due to many different factors. This means that varying these factors, it is possible to affect the resulting blood structure and quality. But nowadays only a little is known about these factors and principles of autotransfusion systems that affect blood quality. Recently, a number of special studies have been performed to discover parameters that can seriously affect the quality of the product of systems for direct retransfusion. And using the data that was received during these tests it is possible to make necessary changes in the process of direct autotransfusion that allow improving the quality of the purifying phase. But it is also possible to exclude the washing phase from the process of direct autotransfusion completely, which can also give better results. However, these tests also have revealed that autotransfusion systems produce blood of inadequate quality. Most of the parameters of direct autotransfusion products were still very poor. So, many systems and filters that are used in them do not provide needed quality of purification and, thus, are not recommended for processing the blood that was drained from the surgical field. And it is highly recommended not to use the blood produced from direct autotransfusion systems that have been tested for retransfusion.