The distribution of nitrogen fractions in the organs of King Edward potato plants harvested at intervals during the growing season has been determined. A general picture of the nitrogen distribution is presented and certain problems suggested by the data are discussed.Each organ of the plant shows a uniformity in its nitrogenous composition during the whole season of active growth. The seed tubers are characterized by their high content of non‐protein nitrogen. This fraction yields the greater part of the nitrogen withdrawn from the seed tubers; the amide, amino and ‘other nitrogen’ fractions all being markedly depleted. The severely depleted tubers retain some 20% of their initial nitrogen content.The roots are rich in non‐protein nitrogen, in which nitrate nitrogen is an important fraction. The roots from ammonium sulphate‐treated plots had a higher total nitrogen content than those from untreated plots, due to accumulation of ammonia nitrogen.The ‘tops’ have a higher nitrogen content and a higher proportion of protein than the roots. There is an increase in protein content and a decrease in non‐protein nitrogen in passing from stems, to petioles, to leaf laminae. The depleted tubers and roots and stems have a uniform low‐protein content of the order 0.4‐0.6 mg. protein nitrogen per g. fresh weight.Asparagine and glutamine occur in approximately equal amounts in the seed tubers and roots. Glutamine is more completely withdrawn than asparagine from the tubers, and in the ‘tops’ it constantly exceeds asparagine in amount.A study of the concentration gradients, from leaves to petioles, to stems, to stem bases and new tubers, of the fractions of the non‐protein nitrogen focuses attention upon the ‘other nitrogen’ as containing the organic nitrogen most actively involved in translocation.The concentration and total content of the glycoside solanine in the different organs has bee