The complexation between an 18-residue zinc finger peptide of CCHC type (CCHC = Cys-X2-Cys-X4-His-X4-Cys, X = variable amino acid) from the gag protein p55 of human immunodeficiency virus type 1 (HIV-1) and various transition metal ions was studied by means of circular dichroism spectroscopy and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). A correlation between the complexation behavior in solution and in MALDI-MS could be established. It was shown that MALDI-MS is a fast method suitable for studying metal binding properties of zinc finger complexes.