Premature infants and neonatal patients who require platelet transfusions may develop circulatory overload when administered a 50-ml unit of platelet concentrate. We evaluated the influence of centrifugation and resuspension steps used to reduce the volume of stored platelet concentrates on platelet properties by in vitro methods and by determining post-transfusion increments in neonatal patients. In vitro studies were conducted with platelet concentrates stored at 20 to 24 degrees C for 1 and 5 days in CLX (Cutter) and PL732 (Fenwal) containers and for 1 and 2 days in PL146 containers (Fenwal). With platelets stored in any of the three containers, platelet morphology, mean platelet volume, hypotonic stress response, synergistic aggregation, and platelet factor 3 activity were not affected by the processing steps. The centrifugation and resuspension steps did not cause an enhanced discharge of lactate dehydrogenase from platelets. Similar results were obtained when the platelet concentrates were stored on either a flatbed or an end-over-end tumbler agitator. The in vitro platelet recovery following volume reduction was at least 85 percent. In vivo studies were conducted with platelets stored in the PL732 and PL146 containers. Infusion of platelet concentrates after volume reduction produced a mean corrected increment of 18,947 +/- 14,824 when platelets were stored in the PL146 container and 16,178 +/- 15,699 when platelets were stored in the PL732 container. These results indicate that the volume of stored platelet concentrates can be reduced in a manner which maintains platelet properties.