The Beckman centrifugal elutriation (CE) system is modified for the separation of platelet-rich plasma (PRP) from human and rabbit blood. The Beckman separation chamber is found inadequate for this purpose, and a new chamber of conical shape has been developed. Optimal flow rate for separating PRP from whole blood with the new chamber of 11.3 ml capacity is 3.5 ml/min while centrifuging at 2500 rpm or 700 g. Collection process takes about 4 minutes. This new process is based on the principle of centrifugal counterflow displacement and filtration, and is different from the CE process which is based on counterflow centrifugation and differential elution. About 90% of total platelets are recovered with this new process. The collected samples are free of leucocytes and contained only a few erythrocytes. Platelets collected by either differential centrifugation (DC) or new procedures are found to be similar in morphological characteristics, both being discoidal. Other characteristics such as aggregation response induced by ADP or epinephrine, serotonin-14C secretion, and survival of autologous platelets in rabbits are also found to be similar. However, ATP release induced by ADP is consistently higher from platelets prepared by our procedure than from those prepared by the DC procedure.