The binding of polyamines, including spermidine ( 1 ) and spermine ( 2 ) , to poly [ d (G-C) * d( G-C) ] was probed using spectroscopic studies of anthracene-9-carbonyl-N'-spermine (3 ) ; data from normal absorption, linear dichroism (LD ) , and circular dichroism (CD) are reported. Ligand LD and CD for transitions located in the DNA region of the spectrum were used. The data show that 3 binds to DNA in a manner characteristic of both its amine and polycyclic aromatic parts. With poly [ (dG-dC) -(dG-dC) 1, binding modes are occupied sequentially and different modes correspond to different structural perturbations of the DNA. The most stable binding mode for 3 with poly[ d(G-C) -d(G-C)] has a site size of 6 f 1 bases, and an equilibrium binding constant of (2.2 f 1.1) X 107M-' with the anthracene moiety intercalated. It dominates the spectra from mixing ratios of approximately 133:l until 6:l DNA phosphate: 3 is reached. The analogous data for poly[d(A-T) -d ( A -T ) ] between mixing ratios 36:l and 7:l indicates a site size of 8.3 f 1.1 bases and an equilibrium binding constant of (6.6 t 3.3) X 105M-'. Thus, 3 binds preferentially to poly[d(G-C )d (G-C ) ] at these concentrations.