Several small, acid-soluble, basic peptides with anti-microbial properties have been isolated from maize (inbred B73) kernels. One of these peptides (MBP-1) has been purified to homogeneity and characterized. The peptide has a molecular weight of 4127.08 as determined by plasma desorption mass spectroscopy, has no free cysteines, and is predominantly alpha-helical as determined by circular dichroism. The primary sequence of the peptide (33 residues) has been determined by Edman degradation and shows no homology to the thionins, a group of cysteine-rich peptides found in some cereals including wheat, barley, and sorghum, as well as several dicot species. Like the thionins, however, MBP-1 has been found to have antimicrobial properties in vitro. MBP-1 inhibits spore germination or hyphal elongation of several plant pathogenic fungi, including two seed pathogens of maize (Fusarium moniliforme Sheld. and Fusarium graminearum (Gibberella zeae (Schw.) Petsch)), and several bacteria, including a bacterial pathogen of maize (Clavibacter michiganense ssp. nebraskense). A synthetic MBP-1 peptide, air-oxidized and purified by reverse phase chromatography, was equally antifungal as compared with the naturally occurring peptide.