LL-37/hCAP-18 is an important part of host defense. Several diseases in human are characterized by impairment in the function of LL-37/hCAP-18 peptide. We examined the expression of LL-37/hCAP-18 in a panel of hematopoietic cell lines representing multiple cell lineages. LL-37/hCAP-18 expression at mRNA level was detected and varied among six of nine cell lines. The level of Raji cells was about eight folds higher than that of Ramos cells. However, only two cell lines, J6-1 and U937, expressed protein products. We also investigated LL-37/hCAP-18 protein in nine leukemia and three idiopathic thrombocytopenic purpura (ITP) patients via immunocytochemical staining. The rate of LL-37/hCAP-18 positive cells ranged from 60 (ITP) to 0.5% (M5). These data suggested that the low translation efficiency of LL-37/hCAP-18 expresses in some leukemia cells might be one of the reasons that leukemia patients were susceptible to infection.