Using a paired study, in vivo and in vitro characteristics of apheresis platelets collected on a cell separator and single-donor whole-blood (recovered) platelets via platelet-rich plasma (PRP) were compared after storage for 5 days in similar plastic containers. Autologous platelets from each of 12 volunteers were labeled with "'Indium after storage and reinjected. There was no significant difference in circulating recovery between platelets prepared by the two methods, and only one of five models of survival showed a significant difference. Hypotonic shock recovery was significantly better in apheresis than recovered platelets (57.0% and 32.4%, respectively), whilst aggregation to ADP at 3.2 pM and 32 p,M was significantly higher in recovered than in apheresis platelets (17.0% and 45.2% versus 7.8% and 32.9%, respectively). Lactate dehydrogenase (LDH) content was significantly higher in recovered platelets (143.3 versus 77.1 IU/lO" platelets), but LDH release was similar (15.0% cf. 12.6%). There was no significant difference between the two platelet preparations for platelet concentration, pH, aggregation with the calcium ionophore A23187 or collagen plus epinephrine, or ATP content or release. 8-TG release was lower in apheresis platelets. Neither product was consistently better than the other for the parameters tested, but apheresis platelets have the advantage of lower donor exposure to the patient.