Surface-enhanced resonance Raman spectroscopy was employed to study the interaction of hypericin with DNA and its model molecules poly(rA) and poly(rG). The obtained results clearly demonstrate that hypericin actually interacts with DNA and that terminal hydroxyl and carbonyl groups are directly implicated in this interaction. A detailed study of DNA structural marker bands in the 600-850 cm(-1) region reveals that guanine plays a crucial role in this interaction. This deduction was confirmed by studying the interaction of hypericin with poly(rG) complex, in which evident changes concerning both hydroxyl and carbonyl groups bands of hypericin and guanine ring breathing band of the polynucleotide can be observed. In view of these results, a model for the hypericin-DNA interaction is proposed.