The efficiency of stored platelet transfusion was evaluated in terms of clinical status in 141 thrombocytopenic patients. In a paired prospective study in which fresh platelets were used as controls, clinical efficiency was assessed on the basis of the ability to increase platelet count (recovery) and the time to the next transfusion (D). In 48 clinically stable patients, recovery of fresh and stored platelets was similar (47% and 41%, respectively) and the interval to the next transfusion was D4 and D3. In contrast, 27 patients who had bacterial infections showed significantly different recoveries (24%/5%) and the interval to the next transfusion was D3/ D1 for fresh and stored platelets respectively. Similarly, in 16 patients who were treated concurrently with amphotericin E, 18 other patients with graft-versus-host disease, nine with splenomegaly and four with veno-occlusive disease (VOD), fresh platelets performed better than stored platelets, showing recoveries of 27%/18%, 29%/15%, 16%/3% and 15%/2%. Furthermore, the need for retransfusion within 24 h was significantly increased with stored platelets. In 19 patients with anti-HLA alloimmunization who were transfused with HLA-matched fresh and stored apheresis platelet concentrate (APC), efficiency was similar (38%/36% and D4/D3). This study indicates that the storage induces an impressive decrease in the in-vivo platelet recovery and survival in patients with certain clinical conditions.