Characteristics of assimilation and transport of nitrogen (N) in tulip plants were investigated mainly by a ¹⁵N tracer technique. Tulip roots accumulate a large amount of N (ca. 90 mgN/gDW) during winter, if N is available in the medium. The accumulated N in the roots originated mainly in absorbed N from the medium rather than from the bulb storage N. During the winter season, the accumulated N in some roots was not readily translocated to the other roots, suggesting that the nitrogen be accumulated independently in each root. The accumulated N remained in soluble forms, especially glutamine was a major constituent. After sprouting in spring, the accumulated N in the roots was rapidly consumed for growth of leaves and stems. Some part of this N was redistributed to bulblets as the plants got matured. The behavior of N accumulated in the roots during winter was basically similar to that of the bulb storage N. Thus, it may be concluded that the physiological role of the N accumulation in roots in to provide a sufficient amount of N required for a rapid growth of leaves immediately after sprouting. During this period, 4-methyleneglutamine was a major amino compound in leaves, stems and roots. The presence of this amide appeared to be a temporary storage of N in vegetative organs of tulip plants. The transport from of N in xylem was mostly glutamine, and 4-methyleneglutamine was not detected. A high accumulation (20-120 mg/gDW) of a novel organic acid, 2-ox-4-methy1-3-pentene-1, 5-dioic acid was found in leaves and stems. This acid seems to be a deamidation and deamination product of 4-methylenglutamine.