Greater numbers of platelets are recovered during discontinuous flow centrifugation than can be simply accounted for by the decrease in total circulating platelets in the donor. There is a linear relationship between the logarithm of the circulating platelet count and the number of plateletpheresis bowls filled. The disappearance of platelets from the peripheral circulation occurs at a greater rate in splenectomized donors than in normal donors, and the rate of platelet disappearance in normal donors is less than what would be expected if there were no in vivo platelet storage pools. The data suggest the redistribution of platelets from the spleen in normal donors during the time course of the procedure.