Surgically removed spleens from 14 subjects were perfused to determine their platelet content. Some patients had Cr51 labeled platelets prior to surgery, and radioactive platelet recoveries were also obtained. A sizable pool of splenic platelets has been demonstrated, which seems dependent on splenic size only. Increase in size of this pool in splenomegaly (and not suppression of thrombopoiesis) may be the sole reason for thrombocytopenia. A dynamic exchange between splenic and circulating platelets appears to be present. Awareness of the existence of a splenic platelet pool is important in considering variation in platelet survival and other platelet dynamic studies, especially in the presence of splenomegaly.