In order to acquire the cDNA of a small molecular peptide with biological activity, the cDNA encoding human defensins was isolated from total RNAs of peripheral leukocyte in a patient with chronic myelogenous leukemia by the RT-PCR method, about 280 bp in length. The RT-PCR products were cloned into the pUCm-T vector, and may be used to construct a novel fusion protein, which contains human defensins and human bactericidal permeability increasing proteins.