While the production of a subcellular particle that can be used as a basic building block for clot formation may be a significant adaptive advantage for mammals, little is known about the exact process by which platelets are produced. Studies of platelet heterogeneity suggest that platelet production is regulated to maintain a constant platelet mass. The number of platelets produced in a given interval is determined primarily by the number of cells differentiating along the megakaryocytic pathway and changes in the rate at which platelets are produced take several days to occur. In contrast, the mean platelet volume (MPV) appears to be determined by the conditions under which the platelets are produced and can be increased within hours of a change in platelet demand. This latter observation, coupled with the observation that megakaryocytes are active, motile cells responsive to a variety of humoral agonists suggests that platelet production is a dynamic process which is under tight regulatory control. Various issues of platelet production are considered in relationship to these observations. An approach to establishing a test model for platelet release is discussed.