DNA-binding strengths of three anthracene-9,10-dicarboxaldehyde hydrazones were examined by spectral shifts of the drug-DNA combinations, spectral titration by Scatchard plots, elevation of DNA melting temperature during complexation and comparison of spectral shifts in the presence of DNA's having variable base contents. Dissociation of the DNA-complexes was also observed. The results showed a strong degree of binding by the three compounds. They did not exhibit noticeable base-pair specificity, but both associated with and dissociated rapidly from DNA. Scatchard plots for DNA association indicated two types of binding; the stronger was most likely due to intercalation of the planar anthracene ring into the DNA double helix. No direct correlation can be drawn between the observed anti-cancer activities and DNA binding affinities of these compounds in vitro.