A newly developed adsorption filter has been evaluated for the removal of white cells (WBCs) from platelet concentrates. It consists of surface-modified polyester fibers and can be used at the patient's bedside. WBC mean removal rate was 98.8 +/- 0.9 percent, and platelet recovery was 99.0 +/- 0.7 percent. The aggregation curves (ADP, collagen) and hypotonic shock response of platelets were not influenced by the filtration, and the plasma electrolyte and lactate dehydrogenase concentrations were unaffected. Transmission and scanning electron micrographs showed no difference in platelet ultrastructure before and after filtration. Determination of posttransfusion platelet recovery did not reveal any significant difference from that of nonfiltered platelets. The tested filter seems to be a suitable device for WBC depletion of single-donor platelet concentrates at the bedside.