The aim of this study was to observe the difference in respect to the leukocyte reduction efficiency and quality of fresh-frozen plasma (FFP) from filtered whole blood between two types of in-line filters wherein only filter materials were surface modified by the two methods respectively. Whole blood was kept in refrigerator and filtered within 6 h of collection at ambient temperature. Samples were taken pre- and post filtration for analysis of WBC numbers, coagulation factors and complement activation (n = 8 for each type of filter). All filtered units contained < 2. 5 x 10(6) residual leucocytes. RBCs recovery was over 93%. No significant difference between group A and B was seen. But group B appeared to take longer time for filtration than did group A (9'29" vs. 8'01"). Neither group A nor group B showed statistically significant losses of total protein, album, IgG, IgM, fibrin, factors VIII, IX, vWF and C3 (P > 0.05). Factor V, XI and AT-III decreased significantly in two group filters. Group B showed more significant losses of IgA content and factor V activity than did group A, which appeared to be related to the difference in surface character between group A and group B filters. These two types of filters could remove leukocytes effectively, and no significant changes were observed in the quality of FFP from the filtered whole blood. It is presumed that the filter material with better bio-compatibility will give a high recovery of plasma protein and coagulation factors after filtration.