The comparative study of the interaction of ethidium bromide, acridine orange, and isoquinoline alkaloids such as sanguinarine and berberine with DNA in aqueous solutions using the optical spectroscopy methods is presented. The dependences of the spectral characteristics of ligands on the concentration ratio P/D between the DNA base pairs and ligands molecules in solutions are considered. The character of binding is found to depend on P/D. The parameters of the binding with DNA are determined for the external binding and the intercalation, by using the modified Scatchard and McGhee-von Hippel equations. The influence of a ligand form on binding ways is shown.