Patients undergoing allogeneic bone marrow transplantation (BMT) were randomized into two groups. One group (n = 21) received single donor platelet concentrates (PC) that were as fresh as possible, the other group (n = 18) received single donor PC stored for 2 to 5 days. Actual mean storage times for PC were 1.12 +/- 1.25 (mean +/- SD) and 2.67 +/- 1.30 d, respectively (p < 0.001). The total need for platelets during 60 d after BMT in patients receiving fresh PC was 22.1 +/- 17.8 x 10(9) platelet/liter blood volume/d, and for stored PC 29.2 +/- 19.2 x 10(9) platelets/liter blood volume/d (n.s.). A multiple regression analysis of the data showed no correlation between PC storage time and the PC requirement (p = 0.85). Posttransfusion corrected count increment (CCI) at 1 hour was 10.4 +/- 5.1 for PC stored 0-1 d, 10.3 +/- 7.0 for PC stored 2-3 d, and 11.4 +/- 9.2 for PC stored 4-5 d. The corresponding CCI, at 18 h were 6.5 +/- 4.4, 5.4 +/- 3.3 and 6.8 +/- 4.6. We conclude that there is no major difference between fresh and stored single donor PC.