Platelet quality after storage strongly depends on the pre-storage quality as well as on the storage conditions determined by the storage container. In this paired study, we evaluated two different containers (MedSep CLX™ and Delmed DPL-110). The Fresenius AS104 cell separator was used to prepare 17 platelet concentrates that were split and distributed into the containers to be compared. Cell counts, blood gas analysis, morphological scores, glucose and lactate levels, platelet activation, and platelet aggregation were measured before splitting ar the day of preparation and after storage ar day 3 and day 5. Ar day 3, there was no significant difference between the two bags apart from increased lactate and decreased pCO2 concentrations in the CLX™ bags. At day 5 there were significantly higher lactate concentrations, pO2 levels, and aggregation after stimulation in the CLX™ group, while the glucose and pCO2 concentrations were significantly lower in these platelet concentrates as compared to the DPL-110 group. However, these parameters did not influence the functional parameters tested. While the platelet quality decreased during storage in all bags, the functional changes were nearly identical in both bags tested. We conclude that both bags are equivalent for 5-day storage of platelet concentrates. ©2001 Wiley-Liss, Inc.