Single-donor platelet concentrates (PC) were prepared in 80-120 ml plasma and stored in two polyolefin bags after addition of 250 ml plasmalyte, a simple, glucose-free synthetic medium that was previously used for platelet storage; when compared to PC stored in plasma, PC stored in plasmalyte, showed similar platelet quality, morphology and function after 5 days of storage. In vivo increments observed after transfusion of PC stored for 5 days in plasmalyte were similar to those observed after transfusion of 1-2 day old PC stored in plasma. Moreover, transfusion of 5-day old PC stored in plasmalyte was associated with correction of prolonged bleeding times in all 3 of the 3 patients evaluated. It is concluded that plasmalyte seems to be promising as a medium for single-donor PC storage.