Nine Co(II) complexes of the type [Co(NN)(n)(N'N')(3-n)] Cl(2)center dot zH(2)O (where NN, N'N' = 1,10-phenanthroline, 2,2'-bipyridine, 4,7-diphenyl-1,10-phenanthroline) were prepd. and characterized by UV, IR and NMR spectroscopies and studied for antitumor activity against human cancer cell lines and against some strains of bacteria and fungi. The complexes with 4,7-diphenyl-1,10-phenanthroline showed strong activities against tumor and bacterial Gram-pos. bacteria cells. Interaction of Co polypyridyl complexes with ATP were also examd. by spectroscopic methods. No antifugal activity of the complexes was obsd.