Interaction of methyl green with the oligonucleotide 5-dGGAAAAGG-[T4]-GGAAAAGG-[T4]-CCTTTTCC (where [T4] is a nucleotide sequence of four thymines) in hairpin duplex and in intramolecular triplex structures has been studied by circular dichroism. We found that methyl green binding to the duplex form shows a complex pattern, exhibiting an exciton contribution when the number of bound molecules increases. Differences between this pattern and previously published results on other DNAs reveals the presence of different types of complexes. In contrast to previous findings with the triple helix poly(dA).2poly(dT) we show that the methyl green is not toallly excluded from this triplex structure made of Pur:Pur:Pyr triplets.