This work carried out a study on the interaction between harmine and oligonucleotide d(GTGCAC)(2). The binding thermodynamic parameters were obtained by ITC method. Harmine binds to oligonucleotide duplex d(GTGCAC)(2) in a fashion of intercalation mode and specific interaction and nonspecific interaction exist in the binding process. H-1 NMR experiments indicate that oligonucleotide d(GTGCAC)2 is a generally self-complementary B-type duplex molecule, and harmine binds to DNA duplex d(GTGCAC)(2) at the side of methoxyl group preferentially in a mode of intercalation. (C) 2003 Elsevier B.V. All rights reserved.