A monomeric 9.4-kDa peptide with antifungal activity was isolated from seeds of Phaseolus vulgaris cv Legumi secchi by using a protocol that involved affinity chromatography on Blue-Sepharose, ion exchange chromatography on Q-Sepharose, and gel filtration on Superdex 75. It was adsorbed on Blue-Sepharose and unadsorbed on Q-Sepharose. Its N-terminal sequence resembled those of other leguminous defensins. It impeded mycelial growth in the fungi Helminthosporium maydis, Rhizoctonia solani, Mycosphaerella arachidicola, and Fusarium oxysporum with an IC50 value of 9.5, 3.5, 1, and 9.2 mu M, respectively, but there was no effect on Valsa mali. SYTOX Green uptake by R. solani indicated that the antifungal peptide induced fungal membrane permeabilization. In contrast to the majority of previously reported defensins/defensin-like peptides, Legumi secchi antifungal peptide did not reduce the viability of MCF-7 breast cancer cells and HepG2 hepatoma cells or inhibit HIV-1 reverse transcriptase, indicating a dissociation between antifungal, antiproliferative and HIV-1 reverse transcriptase inhibitory activities.