The innate immune system produces a number of effector molecules that are important for protection against bacterial infections. Neutrophils and antimicrobial peptides are major components of innate defense with the capacity of rapid bacterial killing. Patients with severe congenital neutropenia (SCN) experience recurrent and chronic infections despite recombinant G-CSF-mobilized neutrophils. We have shown previously that these neutrophils are deficient in that they lack the antimicrobial peptide LL-37. Here, we show that pro-LL-37 mRNA is not expressed in neutrophil precursors from patients with SCN, although the gene and promoter region for pro-LL-37, CAMP, does not display any mutations. The hormonal form of vitamin D3 [1,25(OH)2D3] induced the expression of pro-LL-37 in isolated neutrophil progenitors and in EBV-transformed B cells from patients with SCN, whereas all-trans retinoic acid only induced expression in transformed B cells. These results demonstrate that myeloid cells of patients with SCN can produce pro-LL-37, suggesting that other pathways are impaired.