A series of laboratory culture experiments was designed to investigate uptake of phosphorus and nitrogen by roots and shoots of Myriophyllum spicatum in a number of lake water/substrate and nutrient medium/substrate environments. The plants were compared with respect to biomass, physical dimensions, and total P and N in the plant tissues. It appears that Myriophyllum spicatum can meet its requirements for N by root uptake from the sediment as well as by absorption from the water itself through stem and leaf tissue. It was also seen that Myriophyllum can absorb considerable quantities of P from the sediment via the root system and transport it to the shoot regions of the plant. Growth data suggest that N was growth—limiting for sand—grown plants in nitrate—deficient media, even though tissue N was high. Growth was not decreased in low—phosphate media, suggesting that phosphate—limiting conditions were probably not attained in these experiments. A synergistic relationship between P and N was noted; P in the water clearly affected the ability of Myriophyllum plants to take up nitrate from the water. These data suggest that the limiting concentration of nitrate for Myriophyllum might vary considerably depending in part on the phosphate concentration.