Thionins are plant antimicrobial peptides with antibacterial and antifungal activities. Thionin Thi2.1 cDNA from Arabidopsis thaliana was expressed in BVE-E6E7 bovine endothelial cell line and its activity was evaluated against Escherichia coli, Staphylococcus aureus, Candida albicans and different mammal cell lines. Total protein (2.5 mu g) from conditioned medium (CM) of clone EC-Thi2.1 inhibited the growth of E. coli, S. aureus (> 90%) and C. albicans strains (> 80%) in relation to the CM from control cells. Also, CM of EC-Thi2.1 inhibited the viability of several transformed and normal mammal cell lines (38-95%). These results suggest that thionin Thi2.1 is an antimicrobial peptide that could be use in the treatment of mammalian infectious diseases.