Leukocyte poor RCC's (LP-RCC) are indicated in chronically transfused patients in order to prevent non-hemolytic transfusion reactions and HLA alloimmunization. In this study buffy coat free red cell concentrates (BCF-RCC) in additive solution (SAG-M) stored for four weeks were leukocyte depleted by filtration with three different filter systems (Erypur Optima (E), Sepacell R500 B (S) and, Pall RC, 50 TM (P)). The BCF-RCC's were prepared using 'bottom and top (BAT)' systems and automatic separation containing about 20% leukocytes and 5% platelets of fresh whole blood. The leukocyte concentration could be reduced to less than 5 x 10(6) per RCC with all filter systems equally: Leukocytes/RCC's: E .58 +/- .94, S .36 +/- .55, P .55 +/- .69 x 10(6). The leukocyte depletion was even in case of filtering two RCC's through one filter (double filtration) efficient enough in order to keep leukocyte contamination below the 'critical immunogenic load for leukocytes (CILL)'. But significant differences concerning the damage of red cells (free hemoglobin, LDH, HBDH) were measured which were even considerable: free hemoglobin E = 3.69 +/- 2.28, S = 1.31 +/- 1.24, P = 3.58 +/- 2.34 g/l. Double filtration was only performed with filter system S showing the best blood compatibility. But the second BCF-RCC also showed considerable hemolysis. Therefore, double filtration of RCC's only seems to be indicated under optimal conditions with blood compatible filters for selected patients. Bed side filtration cannot be recommended because of the risk of hemolysis that makes quality control necessary.(ABSTRACT TRUNCATED AT 250 WORDS)