The legume lectins are a large family of homologous carbohydrate-binding proteins. Their carbohydrate specificity and quaternary structure vary widely. The carbohydrate binding activity of legume lectins depends on the simultaneous presence of calcium and transition-metal ions, especially the Mn2+ ion. In the present work, thermal stabilities of Mn2+ binding sites in pea, lentil, soybean and kidney-bean lectins have been studied by electron spin resonance spectroscopy in the temperature range of 120-400 K in different atmospheres. The evolution of parameters, such as the line width, peak-to-peak intensity associated with the hyperfine transition [m (I) (+5/2) -> m' (I) (-5/2)] at the lowest magnetic field side of the central electron transition [m (S) (+1/2) -> m' (S) (-1/2)] of the Mn+2 ion, g-factor and hyperfine splitting was evaluated. Annealing was also performed at high temperatures (353, 373, 383, 403 and 443 K) and the oxidation activation energy of Mn2+ ions in the indicated legumes was determined.