Abstract: The antimicrobial activity of bovine bactericidal/permeability-increasing protein (bBPI)-derived synthetic peptides against mastitis-causing Gram-negative bacteria was evaluated. Three peptides were synthesized with sequences corresponding to amino acids 65-99 (bBPI65-99), 142-169 (bBPI142-169), or the combination of amino acids 90-99 and 148-161 (bBPI90-99,148-161) of bBPI. The bBPI90-99,148-161 peptide demonstrated the widest spectrum of antimicrobial activity, with minimum inhibitory (MIC) and bactericidal (MBC) concentration values ranging from 16-64 ?g/ml against Escherichia coli, Klebsiella pneumoniae, and Enterobacter spp, and 64-128 ?g/ml against Pseudomonas aeruginosa. None of the peptides exhibited any growth inhibitory effect on Serratia marcescens. The antimicrobial activity of bBPI90-99,148-161 was inhibited in milk, but preserved in serum. Finally, both bBPI142-169 and bBPI90-99,148-161 were demonstrated to completely neutralize LPS.