Addition of nitrate N to clover grown in agar generally resulted in a decrease in number of nodules formed when the concentration exceeded 2-3 parts per 100,000. However, the response of the plant to nitrate addition was erratic, and significant decreases were not always noted. Whenever decreases were observed, the effect appeared to be independent of whether nitrate was added at the start or periodically. However, the most consistent depression of nodule formation was noted in the series in which the nitrate was added over a period of 5 wks. Complete prevention of nodule formation was not effected by even the highest concentration of nitrate N used, viz., 1.6 parts per 10,000. Distribution and size of nodules were markedly affected by all concentrations used. Addition of even small quantities of nitrate brought about formation of scattered nodules, largely of the round type, on the secondary roots; normally the nodules are mostly of the long type and occur on the tap root near the crown. Size of nodules was decreased as quantity of nitrate was increased. These results were independent of the method of adding nitrate, provided a certain minimum quantity of N was available at the start. All concentrations of nitrate N used markedly decreased fixation of free N. If the nitrate N added was insufficient for the needs of the plants, the deficit was made up by fixation of atmospheric N. However, as soon as an excess of N was provided, fixation appeared to be completely suppressed, even though nodules were present.