Antimicrobial peptides, including beta-defensins, are thought to be effective agents against opportunistic infections. In humans, three beta-defensins have been identified. The first human beta-defensin, hBD-1, is predominantly expressed in epithelia of the urogenital tract and has been reported to be constitutive. The second and third human beta-defensins, hBD-2 and hBD-3, were isolated from psoriatic skin and found to be predominantly expressed in skin and respiratory tract. Of note, the hBD-2 gene expression is inducible by various proinflammatory agents such as TNF-alpha, IL-1 beta, IL-8, LPS, bacteria, and yeasts. It has been shown that LPS-induced expression of hBD-2 in human tracheobronchial epithelial cells requires CD14, which may complex with Toll-like receptors (TLRs) to ultimately activate NF-kappa B. In addition, beta-defensins have been recently reported to promote immune responses by recruiting dendritic and T cells. Defensins may play a key role in the mechanism of host defense and innate immunity. These defensins, including hBD-2, might provide a new therapeutic approach to infectious diseases.