World sugarcane production is increasing rapidly as a biofuel. In some areas in Brazil, sugarcane has been grown continually over very long periods without N fertiliser inputs. Therefore, the occurrence of N fixation has been suspected. However, quantitative studies seeking to identify the N~2~ fixation sites in the plant and to record the translocation of fixed N around the plant have not yet established. A ^15^N~2~ gas tracer experiment was conducted using young sugarcane plants to investigate the sites of N~2~ fixation and also to explore the possibility of translocation of the fixed N among the plant's major organs. Young sugarcane plants (_Saccharum officinarum_ L.) about 40 cm high and some 14 days after sprouting from a stem cutting were exposed to ^15^N~2~ labeled air in a 500 mL plastic cylinder for 7 days. Following the 7-day ^15^N~2~ feeding, some plants were potted and grown on in normal air for a further chase period. The incorporation of ^15^N into the shoot, roots, and stem cutting was analysed at day-3, and day-7 of the labeling period and at day-14, and day-21 during the chase period. After 3 days of ^15^N~2~ feeding, the % of N derived from the ^15^N labeled air in the shoot, roots and stem cutting were 0.027%, 2.22% and 0.271%, respectively. The roots showed the highest N fixing activity followed by the stem cutting, while the incorporation of ^15^N into the shoot was very low. After 21 days about a half of the N originating in the stem cutting had been transported to the shoot and the roots. However, the ^15^N fixed either in the roots or in the stem cutting remained in the original parts and was not appreciably transported to the shoot
