Elevated anaphylatoxin concentrations have been found in fresh frozen plasma packs produced by apheresis. The aim of this study was to investigate anaphylatoxin generation during apheresis production in relation to two frequently used techniques: employing either centrifugation alone or centrifugation with simultaneous filtration. The concentrations of C3a. C5a and sC5b-9 were measured in 50 plasmas after apheresis and before freezing generated by combined centrifugation and filtration and in 50 plasmas generated solely by centrifugation and in the corresponding 100 donors before apheresis. The median C3a concentration increased during apheresis by centrifugation alone from 62 (donor) to 380 micrograms L-1 (FFP pack) and during apheresis by combined centrifugation and filtration from 70 to 992 micrograms L-1. The median C5a concentration increased during apheresis by centrifugation alone from 0.38 to 0.83 microgram L-1 and during apheresis by combined centrifugation and filtration from 0.29 to 4.9 micrograms L-1. The soluble terminal complement complex increased only by combined centrifugation and filtration apheresis from 162 to 426 micrograms L-1. Complement activation during apheresis by combined centrifugation and filtration is more pronounced than that obtained by the centrifugation method alone. Changes in the construction or the materials used in the membrane-type separation units may reveal possibilities of prevention.