Comparisons of the spectroscopic properties of a number of Ru-III complexes of imidazole ligands provide methods of distinguishing between various types of bonding that can occur in proteins and nucleic acids. In particular, EPR and H-1 NMR parameters arising from the paramagnetism of Ru-III should aid in determining binding sites of Ru-III drugs in macromolecules. Electrochemical studies on several imidazole complexes of ruthenium suggest that imidazole may serve as a significant pi-acceptor ligand in the presence of anionic ligands. Crystal structures are reported on two active immunosuppressant complexes. cis-[(Im)(2)(NH3)(4)Ru-III]Br-3 crystallizes in the triclinic space group P (1) over bar (No. 2) with the cell parameters a = 8.961(2) Angstrom, b = 12.677(3) Angstrom, c = 7.630(2) Angstrom, alpha = 98.03(2)degrees, beta = 100.68(2)degrees, gamma = 81.59(2)degrees, and Z = 2 (R = 0.044). [(1MeIm)(6)Ru-II]Cl-2 . 2H(2)O crystallizes in the monoclinic space group P2(1)/n (No. 14) with the cell parameters a = 7.994(2) Angstrom, b = 13.173(4) Angstrom, c = 14.904(2) Angstrom, beta = 97.89(1)degrees, and Z = 2 (R = 0.052). The average Ru-II-N bond distance is 2.106(8) Angstrom.