We evaluated whole blood integral filtration to produce leucocyte-depleted red cells and plasma by using the WBF1 whole blood filter (Pall Medsep). Whole blood units were filtered after either warm (2-4 h at room temperature) or cold (12-24 h at 4 degrees C) holds. Filtered and control units were processed using either a bottom-and-top or top-top method. Red cells were tested weekly for 6 weeks, and plasma 3 monthly for 12 months. All filtered red-cell packs contained < 5 x 10(6) leucocytes/unit with 71 of 72 containing < 1 x 10(6) leucocytes/unit. No clinically significant differences in red-cell storage parameters were seen, although haemolysis was less and pO2/pCO2 values were better maintained in filtered units. Plasma units contained < 2.5 x 10(3) leucocytes/unit with no significant loss of factor VIII except in the warm hold units processed by the top-top method. There was no evidence of complement or coagulation activation with significant removal of preformed C3a in cold hold units. Plasma storage parameters were maintained at control levels for 12 months.