Nitrogen-fixing activity in two nodulated African legumes, Bambara groundnut (Vigna subterranea L.) and Kersting’s bean (Macrotyloma geocarpum L.), was assessed in the presence of nitrate (NO $ ’) ions in the rooting medium. Nitrogenase activity was unimpaired by the supply of 5 mol m’$ NO $ to both species. Also, large concentrations of ureides dominated the transpiration stream of NO $ -fed plants. Compared to other symbiotic legumes cultured with similar NO $ concentrations, nodule functioning in the tested landraces of Bambara groundnut and Kersting’s bean is tolerant of NO $ ions in the rhizosphere. The potential benefits of such naturally occurring NO $ -tolerant symbioses are substantial, as they would permit inorganic N fertilizer application in intercropping systems without inhibiting N # fixation in the associated legumes. # 1998 Annals of Botany Company