In order to understand the role of coordinated ligands in controlling the biotoxicity of chromium (III), interactions of three types of chromium (III) complexes viz. trans-diaquo [1,2 bis (salicyledeneamino) ethane chromium (III) perchlorate, [(Cr(salen) (H2O)(2)](ClO4); tris (ethylenediamine) chromium (III) chloride, [Cr(en)(3)]Cl-3, and monosodium ethylene diamine tetraacetato mono-aquo chromiate (III), [Cr(EDTA)OH2O)]Na with BSA has been investigated. Spectroscopic and equilibrium dialysis studies show that the two cationic complexes Cr(salen)(H2O)(2)(+) and Cr(en)(3)(3+) bind to the protein with a protein-metal ratio of 1:8 and 1:4. The anionic complex Cr(EDTA)(H2O)(-) binds to the protein with a protein-metal ratio of 1:2. The binding constant K-b as estimated from the fluorescence quenching studies has been found to be 7.6 +/- 0.4 x 10(3) M-1, 3.1 +/-0.2 x 10(2) M-1, and 1.8 +/- 0.2 x 10(2) M-1 for Cr(salen)(H2O)(2)(+), Cr(en)(3)(3+), and Cr(EDTA)(H2O)(-) respectively indicating that the thermodynamic stability of protein-chromium complex is Cr(salen)(H2O)(2)(+) > Cr(en)(3)(3+) approximate to Cr(EDTA)(H2O)(-). The complexes Cr(salen)(H2O)(2)(+) and Cr(EDTA)(H2O)(-) in the presence of hydrogen peroxide have been found to bring about protein degradation, whereas Cr(en)(3)(3+) does not bring about any protein damage. This clearly shows that the nature of the chromium (III) complex plays a major role in the biotoxicity of chromium (III).