In order to investigate the role of frankial siderophores in minimizing metal toxicity, Frankia strains were grown at different concentrations of Mg2+, Cu2+, and Zn2+. Growth was observed up to 500 mmol L-1 Mg2+, 10 μ mol L-1 Cu2+, and 10 μmolL-1 Zn2+ while the maxima were at 200 μmol L-1 Mg2+, 1 μmol L-1 Cu2+, and 1 μmol L-1 Zn2+. The siderophore production was increased up to 500 μmol L-1 Mg2+, 10 μmol L-1 Cu2+, 100 μmol L-1 (hydroxamate type), and 200 μmol L-1 (catecholate type) Zn2+ while maximum production was found at Mg2+ (200 μmol L-1), Cu2+ (10 μmol L-1), and Zn2+ (10 μ molL-1). The results suggested that the growth was protected at higher concentrations of Mg2+ (up to 500 μmol L-1), Cu2+ (10 μ molL-1), and Zn2+ (10 μ mol L-1), possibly due to enhanced siderophore production. Thus, siderophores minimize the metal-induced inhibition of growth in Frankia, likely due to regulation of nutritional imbalances and metabolic processes during adaptation towards metal stress and/or metal toxicity. © 2010 Taylor & Francis.