1H NMR spectroscopy was used in studying the binding of [Pt(en)(phen)]2+ and [Pt(en)(phi)]2+ to the hexanucleotide d(GTCGAC)2. The results indicate that both square planar platinum(II) complexes bind the hexanucleotide by intercalation from the minor groove. This suggests that simple square planar metallointercalators, like organic intercalators, have an intrinsic preference for the DNA minor groove.