To study survival and function of leukocyte-poor platelet concentrates (lp-PC) prepared from buffy coats, random platelet transfusions requested for thrombocytopenic patients were evaluated. The lp-PC issued were stored at 22 degrees C for either 1, 3 or 5 days before transfusion. From 31 transfusions, posttransfusion corrected count increments (CCI), corrected for body surface (m2) and divided by number of platelets transfused (1011), were calculated. The mean +/- SEM of the 1-, 24- and 48- hour CCI was 12.2 +/- 0.45, 11.2 +/- 0.51 and 8.8 +/- 0.58, respectively. No significant differences in CCI 24 h after transfusion were observed for 1p-PC stored for 1, 3 or 5 days. Hemostatic activity was observed in all 9 evaluable patients. It is concluded that platelets from 1p-PC survive well in patients, regardless of storage for 1, 3 or 5 days and that the platelets are hemostatically active after transfusion.