Platelet concentrates (PCs) were prepared from single buffy coats derived from fresh blood and from blood units stored overnight, as well as from buffy coats that were stored overnight. The platelet yield from overnight-stored buffy coats was similar to that of fresh blood or overnight-stored blood. PCs were stored at 20-24°C and on day 5 of storage, platelet aggregation with ADP was tested both at 37 and 25°C. Stored platelets aggregated better at 25°C than 37°C. The maximal aggregation (10 µA/ ADP) of stored platelets from overnight-stored buffy coats was 46±23% (n = 30), while that of stored platelets prepared either from fresh or overnight-stored blood was 27±21 % (n = 29) and 22± 15% (n = 29), respectively. Extracellular lactate dehydrogenase and ammonia levels, as well as elastase activity were similar in stored PCs of different origin. Our conclusion is that PCs prepared from overnight-stored buffy coat might also be suitable for storage and clinical use. In vivo studies are needed to confirm our findings.