Nitrogen use efficiency (NUE) of N fertilizer can be accurately estimated by tracing the fate of soil applied15N‐labeling. However, the quantity of N remobilization from non‐kernel components into kernels in maize (Zea maysL.) plants is difficult to determine. A field experiment involving stem infusion with four levels of enriched15N solution plus non‐infusion or infusion with water was conducted at Ottawa (45°22'N, 75°43'W), Canada to determine the effect of15N atom % enrichment (a.e.) on physiological processes associated with NUE. At anthesis, 30 mL of 35.7 mmol N solution as15NH415NO3at 5.0 (N05), 33.0 (N33), 66.0 (N66) and 99.2 (N99)15N% a.e. was infused into the internode below the primary cob. The control plants were infused with distilled water. Photosynthesis was measured at 2, 4, 6, 24 h and 1 wk after infusion. Plants were sampled and separated into components at 4 d after anthesis (D4A) and at physiological maturity (PM). Dry weight, total N concentration, NH4‐ and NO3‐N, and15N% a.e. of each component were determined. At D4A, the N33 and N66 treatments resulted in component15N enrichment similar to that of N99 treatment. At PM, however, only N66 treatment produced results similar to that of N99. None of the infused15N treatments interfered with ear‐leaf photosynthesis or component NH4‐ and NO3‐N concentrations. Infused15N was easily moved out of the internode where it was infused, into most components, with the majority in the dominant sinks (cob, husk, and kernels). Nitrogen remobilization in both N66 and N99 treatments accounted for 62% of kernel N. These findings indicate that stem infusion is an appropriate approach to study N remobilization. Based on the concentrations investigated in this study, 66% or higher15N% a.e. is required for accurate labeling when soil available N is high.