The relationship between growth of aquatic plants and their nutrient supply is poorly understood. One object was to learn if the Michaelis-Menten model describes the relationship between the uptake of NH4 and the concentration of NH4 in solution. A hyperbola resulted when uptake of NH4 by Ceratophyllum (v) was plotted against the concentration of NH4 in solution (S). Linearity between v and S existed at concentrations less than 7 mg NH4-N(1). This suggested that a model for first order saturation kinetics might be appropriate. However, uptake was depressed by one-half at low temperatures and some of the uptake was apparently related to processes which are not completely passive. Another objective was to determine if hydrophytes could absorb ammonia through the root and rhizome system and, subsequently, translocate the absorbed nitrogen to stems and leaves.