A system is described for the perifusion of cells with a perifusate containing oxygen at concentrations defined by the user. The metabolic competency of cells in this system was assessed by measuring total ATP turnover for human platelets. Human platelets, which are small (radius of 1-2 mu m) anucleate cells involved in blood clotting, maintained ATP turnover over a 4-h period at 37 degrees C. Oxygen concentration in this system was controlled by adjusting the proportions of air-saturated and nitrogen-saturated perifusates. Examples of oxygen consumption and lactate output as a function of oxygen concentration are described. (C) 1998 Academic Press.