Alpha defensins belong together with the ß-defensins to the family of cationic trisulfide-containing microbicidal peptides. They exert their microbicidal activity by permeating the membrane involving the formation of voltage regulated ion channels. Rabbit neutrophils contain large amount of alpha defensins (Neutrophil Defensin) NP 1 - 6. Defensins constitute more than 15% of total protein in rabbit neutrophils and are accumulated in dense cytoplasmic granules. Rabbit neutrophils express all six rabbit alpha-defensins, NP 1 - 6. Among myeloid rabbit alpha-defensins NP 1 - 6, NP 3 - 6 are neutrophil specific, while NP 1 - 2 are expressed in rabbit alveolar macrophages. Defensins are relatively resistant to proteolysis, low pH and boiling. Rabbit neutrophil defensins, whose three-dimensiol structures are very similar to those of human alpha defensins may be helpful in understanding the role of antimicrobial peptides in innate and acquired immunity and in the studies on the role of neutrophils in pathological situations and in various rabbit models of human diseases. Anti NP-5 antibody clone R3 recognizes natural NP-5 in biological solutions, in tissue sections and leukocyte smears fixed with ethanol, methanol/acetone or paraformaldehyde, in flow cytometry analysis of rabbit neutrophils stained by cell permeabilization method and in Western blotting reaction. Furthermore the antibody is capable to recognize synthetic and recombinant NP-5.