Defensins are a family of small cationic, antibiotic peptides that contain six cysteines in disulfide linkage. The peptides are abundant in phagocytes and small intestinal mucosa of humans and other mammals and in the hemolymph of insects. They contribute to host defense against microbes and may participate in tissue inflammation and endocrine regulation during infection. Bioengineered defensins are potentially useful as prophylactic and therapeutic agents in infections.