ABSTRACTShort‐term (1–9 min) nitrate uptake kinetics were measured inThalassiosira pseudonana(Hust.) Hasle&Heimdal grown in nitrate‐limited, ammonium‐limited, and nitrate‐sufficient continuous cultures. For all cultures, maximal nitrate uptake rates did not develop until approximately 3 min after nitrate addition; thereafter, nitrate uptake rates remained constant or declined slightly. The Ksand Vmaxfor the nitrate‐limited cultures were higher at any growth rate than those for the ammonium‐limited or nitrate‐sufficient cultures. Thus, much higher nitrate concentrations would be required to saturate nitrate uptake in nitrate‐limitedThalassiosira pseudonanathan is usually considered necessary. The lack of data for other species grown under a range of environmental conditions makes it difficult to generalize about the effect of preconditioning on nitrat