Results of absorption titration, thermal denaturation, and differential pulse voltammetric experiments suggest that [Co(phen)(2)DPPZ](3+) and [Ni(phen)(2)DPPZ](2+) (phen = 1, 10-phenanthroline and DPPZ = dipyrido[3,2-a:2’,3’-c]phenazine) are both avid binders of calf thymus DNA. On the other hand, while the cobalt(III) complex has been found to effect the photocleavage of the supercoiled pBR 322 DNA, the nickel(II) complex is ineffective under similar experimental conditions.