Published experiments are reevaluated regarding the uptake ratio of dissolved inorganic carbon (DIC) and nitrate in two plankton communities and the resulting elemental ratio of particulate organic matter (POM). The ratios are lower than Redfield values of 6.6 or 7.6 (by atoms); the uptake ratios of dissolved moieties are not measures for the composition of the newly formed POM; and uptake of DIC and nitrate may be entirely uncoupled. The use of closed systems of several 100 L to 1 m−3content is suggested for studies of the underlying mechanism