The prevention of transfusion reactions and transmission of infectious diseases partly relies on the systematic removal of leukocytes from blood products. Apheresis platelets and plasma collected on the Haemonetics((R)) MCS+ collection system require filtration to obtain low levels of residual leukocytes. This filtration step is automated for platelet concentrates, whereas plasma filtration requires sterile docking of a leukoreduction filter. Our experience shows residual leukocyte levels of approximately 10(5) for platelets (the French requirements are 10(6) per unit) and 10(2) for apheresis plasma (no existing standard in France). Leukocyte residuals in platelets are highly dependent on the filtration rate, which should be as slow as possible. Whereas the current method of filtration is convenient for platelets, the connection of an in-line filter for plasma causes some organizational problems and is also associated with a loss of plasma. Haemonetics' latest development, the use of a filtering core bowl, should avoid the requirement for the connection of an additional filter for plasma filtration and will ensure continuous filtration of platelets, reducing, even further, the residual leukocyte count in platelet concentrates. (C) 2001 Elsevier Science Ltd. All rights reserved.