We report the isolation and characterization of a novel peptide with significant sequence homology to beta-defensins from human blood filtrate. The human beta-defensin-1 (hBD-1) is a short basic peptide of 36 amino acid residues. It contains six cysteines forming three intramolecular disulfide bonds. The molecular mass of hBD-1 is 3928.6 Da. Cloning of the specific cDNA confirmed the amino acid sequence of the native peptide. hBD-1 shares the nine conserved amino acids characteristic for beta-defensins from respiratory epithelial cells and neutrophils of cattle and chicken leukocytes. hBD-1 is present in nanomolar concentration in human plasma.