[en] For a farmer to reap benefit from mung bean's (Vigna radiata) capacity to fix N₂, the crop's requirement for N must come mainly from the atmosphere through symbiotic fixation in the root nodules. The aim of this study was to evaluate recommended mung-bean cultivars and advanced breeding lines, and identify high fixers. Preliminary investigations with the ¹⁵N natural-abundance method indicated its utility for measuring N₂ fixation, and the examination of five recommended cultivars and two advanced breeding lines of mung using the ¹⁵N-dilution method showed diversity in N₂ fixation and yield. More than 400 lines of mung bean were screened in soil in cement containers for growth, nodulation, N accumulation and N₂ fixation at 35 days after planting, with the natural-abundance method used to determine N₂ fixation. Genetic variability was observed for all characteristics. Estimates of fixed N ranged from 0-300 mg N/plant. Whereas some lines obtained N mainly from fixation, recommended cultivars apparently obtained their N mainly from soil. The data are discussed in terms of reliability of the ¹⁵N natural-abundance method