An 18-residue peptide, corresponding to the minimum sequence of the N-terminal zinc-finger domain in the nucleocapsid of human T-lymphotrophic virus type I, was synthesized by a solid-phase method and fully characterized. Its ability to complex metal ions (Co(2+) and Zn(2+)) was clearly established by UV-visible spectroscopy and MS. The stability of these complexes was investigated by an original method with HPLC chromatography. Our results show that, even in the presence of air, the Zn(2+) complex is highly stable. In contrast, the Co(2+) complex undergoes a relatively fast degradation due to an intramolecular oxidation leading to the formation of a disulphide bridge between two cysteine residues. The (1)H-NMR analysis indicates that Zn(2+) binds to the Ndelta atom of the histidine residue rather than to the Nepsilon atom. Two-dimensional NMR techniques were used to determine the solution structure of the zinc-finger, illustrated by the existence of turns in the overall conformation.