The binding of Hoechst 33258 with DNA at various ionic strengths of solution and different ligand concentrations has been investigated. Existence of more than one type of interactions of Hoechst 33258 with DNA has been revealed, which were very sensitive to the ionic strength. Hoechst 33258 doesn?t show specificity to AT sequences of DNA at low ionic strength. High affinity binding mode becomes obvious at high ionic strength. The values of binding constants and binding site sizes for revealed strong and weak interactions have been determined.

Key words: Binding constant; Binding site size; DNA - Hoechst 33258 complexes; and Scatchard plot.