With a view to determining nitrogen sink processes, if any, in streams and the factors that govern these processes, nitrogen transport was studied in a 2 km-long, perennial, spring-fed stream during the summer months of 1973 and 1974. Concentrations of ammonium, nitrite and Kjeldahl nitrogen were small but those of nitrate nitrogen were unusually high. However, as the water moved downstream it progressively lost nitrate N. This loss represented 59.4% and 46.7% of the respective inputs during 1973 and 1974. The decrease in the concentration of nitrate N could neither be attributed to dilution nor to nitrogen immobilization during decomposition of organic matter nor to the uptake by aquatic macrophytes. Laboratory experiment showed that the stream sediments have significant, capacity for denitrification of nitrate in water overlying them, even when the water is thoroughly oxygenated. Although the role of riparian plants in the uptake of nitrogen has not been fully elucidated, it seems that denitrification in the stream sediment may act as an important permanent nitrogen sink.