Objective: Fat microemboli are generated during cardiac surgery that are associated with post-operative organ injury. Recently, a fat removal filter has been developed, based on a polyester leukocyte depletion filter. However, the efficacy of such a filter in a clinical setting is unknown. In this study we tested the efficacy of this filter. Methods: Coronary artery bypass patients were randomly divided into two groups. Group I: filtration of cardiotomy suction blood during cardiopulmonary bypass with a fat removal filter (n = 14). Group II: control patients without filtration (n = 14). Filter efficacy was evaluated in group I using biochemical assays and thin layer chromatography of blood samples taken simultaneously before and after the filter. In addition, clinical and biochemical markers for organ injury were determined in both groups. Results: The fat filter removed triglycerides (0.9 +/- 0.08 vs. 0.63 +/- 0.08 mmol l(-1), P = 0.004, paired t-test), leukocytes (4.3 +/- 0.8 x 10(9) vs. 2.3 +/- 0.6 x 10(9) l(-1), P = 0.03), and platelets (116 +/- 26 x 10(9) vs. 75 +/- 21 x 10(9) l(-1), P = 0.003) from the blood samples taken before and after the filter. Chromatography showed a significant reduction in free fatty acids, phospholipids and triglycerides. Clinically, leukocyte counts were similar, but platelet counts were higher (181 +/- 14 x 10(9) vs. 117 +/- 8.6 x 10(9) l(-1) control, P <0.001) in group I on the first postoperative day. Conclusion: The fat filter removed 40% fat, leukocytes and platelets from cardiotomy suction blood during cardiac surgery. A larger scale study is necessary to determine clinical effects on organ damage. (C) 2003 Elsevier B.V. All rights reserved.