The hormonal form of vitamin D 3, 1, 25-dihydroxyvitamin D 3 (1, 25 (OH) 2 D 3), is an immune system modulator and induces expression of the TLR coreceptor CD14. 1, 25 (OH) 2 D 3 signals through the vitamin D receptor, a ligand-stimulated transcription factor that recognizes specific DNA sequences called vitamin D response elements. In this study, we show that 1, 25 (OH) 2 D 3 is a direct regulator of antimicrobial innate immune responses. The promoters of the human cathelicidin antimicrobial peptide (camp) and defensin β2 (defB2) genes contain consensus vitamin D response elements that mediate 1, 25 (OH) 2 D 3-dependent gene expression. 1, 25 (OH) 2 D 3 induces antimicrobial peptide gene expression in isolated human keratinocytes, monocytes and neutrophils, and human cell lines, and 1, 25 (OH) 2 D 3 along with LPS synergistically induce camp expression in neutrophils. Moreover, 1, 25 (OH) 2 D 3 induces corresponding increases in antimicrobial proteins and secretion of antimicrobial activity against pathogens including Pseudomonas aeruginosa. 1, 25 (OH) 2 D 3 thus directly regulates antimicrobial peptide gene expression, revealing the potential of its analogues in treatment of opportunistic infections.