BACKGROUND: The mechanisms of the detrimental effects of perioperative allogeneic blood transfusion are still unclear. Previous studies have suggested a higher incidence of adverse effects after the use of blood stored for prolonged time. Therefore, a possible time-dependent release of various white cell- and platelet-derived bioactive substances in stored human red cell suspensions was studied. STUDY DESIGN AND METHODS: Whole blood (6 units), plasma-reduced whole blood (6 units), and saline-adenine-glucose-mannitol blood (6 units) from 18 unpaid, normal blood donors were stored under standard blood bank conditions at 4 degrees C for 35 days. After refrigeration, samples were collected from all blood bags on Days 0, 2, 5, 9, 14, 21, 28, and 35 of storage. Extracellular concentrations of eosinophil cationic protein, eosinophil protein X, plasminogen activator inhibitor 1, myeloperoxidase, and interleukin 6 were analyzed by enzyme-linked immunosorbent assay and radioimmunoassay. The total intracellular and donor plasma levels of these substances also were analyzed at the time of blood donation. RESULTS: Eosinophil cationic protein, eosinophil protein X, and myeloperoxidase increased 10- to 25-fold (p < 0.05) in a time-dependent manner in whole blood, plasma-reduced whole blood, and saline-adenine- glucose-mannitol blood during storage for 35 days. Plasminogen activator inhibitor 1 increased threefold to sixfold (p < 0.05) in whole blood and plasma-reduced whole blood, but not in saline-adenine- glucose-mannitol blood. Interleukin 6 was not detected in either plasma or samples obtained from the blood bags. CONCLUSION: Stored whole blood, plasma-reduced whole blood, and saline-adenine-glucose-mannitol blood may release white cell- and platelet-derived bioactive substances in a time-dependent manner, which may be related to the detrimental effects of perioperative blood transfusions. Therefore, prestorage white cell reduction should be considered for further improvement of red cell suspensions.