In studying the nitrogen cycle in the sea a consideration of the nitrite concentration in the water is especially useful, because of its intermediate position between ammonia on the one hand and nitrate on the other. Although it is not a stable end-product, its very instability makes it a possible indicator of the state of equilibrium between the oxidation and reduction processes making up the cycle. Its order of magnitude in the water is much smaller than that of nitrate, or even ammonia, but the methods for its analysis are correspondingly more accurate, so that its normal variations may be followed as closely as those of the other nitrogen compounds. In view of the ease with which nitrite determinations may be made, it is surprising that there are not more data on its occurrence in sea water. Raben (1914, 1918) and Brandt (1927) were among the first to report such figures, but their data were only scattered and fragmentary. Orr (1926) reported some analyses of samples from the vicinity of the Clyde Sea, made observations on diatom cultures, and discussed the factors concerned in the appearance and disappearance of nitrite. Harvey (1926) failed to find significant amounts of nitrite in the English Channel or in deeper waters of the Atlantic further south, but noticed their occasional appearance in stored samples. Atkins (1930), however, was able to make a fairly comprehensive study of the seasonal changes in nitrite in the English Channel, finding high concentrations at certain levels and at certain times. Orton (1924), investigating various influences upon the growth of oysters, found moderately high concentrations in samples from Plymouth Sound, Thames Estuary and Helford River. He also followed nitrite changes in the water of storage tanks. In a few cases, figures for nitrite have been reported incidentally, or in connection with other chemical studies of sea water, as by Braarud and Klem (1931), Robinson and Wirth (1934), Rakestraw (1932, 1933), Matsudaira and Yasui (1932, 1933), and in connection with