Platelets were isolated from normal volunteers by discontinuous-flow centrifugation using the Haemonetics Model 30 Blood Processor. The numerical equivalent of about five single units of platelets collected at each pheresis were frozen together in a -80 C mechanical freezer with a 6% final concentration of dimethylsulfoxide (DMSO) as the cryoprotectant. Platelet freeze-thaw-wash recovery in vitro was about 80 per cent and the platelet recovery value depended upon the method used to enumerate the platelets. The 51Cr survival values in vivo were about 50 per cent less than those in fresh platelets. These values were not significantly different from those seen when platelets were isolated from single units of blood by differential serial centrifugation. Transfusion of two and one-half units of freeze-preserved platelets provided an increase in the recipient's circulating platelet count comparable with that from one unit of fresh platelets. The hemostatic effectiveness of freeze-preserved platelets isolated by discontinuous-flow centrifugation has not yet been studied.