] ~ O R THREE DECADES, specialists in transfu. ] ~ sion medicine have become accustomed to preparing, storing, and transfusing red blood cells suspended in synthetic storage solutions. The idea of a simple nutrient solution containing adenine and glucose for this purpose was apparently first described in 1965.1 It is now widely accepted practice. During storage at 4~ red cells maintain their viability longer in these solutions than they do in plasma. Since the first report of Rock et al 2 in 1985, many investigators have directed their efforts toward developing :an analogous solution for platelets. Potential advantages include superior platelet quality after storage; availability of more plasma for fractionation; and the reduction in frequency and severity of transfusion complications related to components of the suspending plasma. Although 9 progress has been slower than was originally hoped, some succ;essful solutions have been developed and are in use in some transfusion services in Europe. The purpose of this review is to describe the events of the last 15 years that have led to our current circumstances. Inevitably, it will reflect the experience (and the biases) of the author. Where strong disagreements have been expressed, these are noted and addressed. Attention is confined to the storage ofplatelets with appropriate agitation at 20~ to 24~ 3 within plastic containers with gas permeability adequate to maintain the oxidative metabolism of the platelets being stored. 4 The optimal method for assessing the quality of stored platelets is the measurement of their capacity to circulate in vivo after reinfusion. Because of the complexity and expense of such in vivo studies, some of the reports described have used in vitro correlates for in vivo viability. 5 Most of the studies reviewed have used platelets prepared by the platelet-rich plasma (PRP) method from units of whole blood. In this method, whole blood is centrifuged at low speed to prepare PRP, which is then centrifuged at high speed to prepare a platelet button, which is resuspended in approximately 50 mL of autologous plasma, yielding a platelet concentrate (PC). A PC made by this method is referred to as PRP-PC. Typically, when PRP-PC have been used with synthetic media, the button is resuspended in medium, leaving a 10% to 20% plasma carryover. In later studies, the buffy coat (BC) method was used, in which the whole blood is centrifuged at high speed to prepare a BC from which a BC-PC is prepared. Finally, two studies used platelet concentrates prepared by apheresis (AP-PC).