We have chemically synthesized tracheal antimicrobial peptide (TAP) with 38 amino acids and examined efficacy of the peptide on various organisms. The synthetic peptide showed potent bactericidal effect on both gram positive and negative bacteria. The action of bactericidal effect was relatively quick and 99.9% of E. coli cells were killed within 90 minutes at a concentration of 2.5 micrograms/ml of TAP. The peptide also showed antifungal activity against both mycelia (Aspergillus fumigatus) and yeast (Candida albicans) forms of fungi. Our domain analysis with a series of synthetic peptides of various lengths indicates that 17 amino acid residues of the C-terminal end is the minimum functional domain of the bactericidal activity.