The. rates of glucose uptake by some species of plankton were determined by 3H-glucose tracer method. Experimental results indicated that the observed glucose uptake at natural sea water concentrations by Platymonas subcordiformis and Brachionus plicatilis was principally a metabolic process fitted with the Michaelis-Menten equation in the range of adaptive temperatures. Heterotrophic uptake by Platymonas subcordiformis was mainly dependent on diffusion at high glucose levels. The uptake by Brachionus plicatilis showed active transport even at high glucose levels, indicating its high heterotrophic activity. The uptake rate by Anemia salina was lower, and its Vm/K ratio was lower than those of the other two species of plankton. The rates of glucose uptake by some species of plankton were determined by 3H-glucose tracer method. Experimental results indicated that the observed glucose uptake at natural sea water concentrations by Platymonas subcordiformis and Brachionus plicatilis was principally a metabolic process fitted with the Michaelis-Menten The uptake by Brachionus plicatilis showed active transport even at high glucose levels, indicating its high heterotrophic activity. The uptake rate by Anemia salina was lower, and its Vm / K ratio was lower than those of the other two species of plankton.