To analyze the microbicidal properties of the HNP1 conformers produced by CNBr cleavage of proHNP1A and proHNP1B, we tested the respective peptides for killing of S. aureus in vitro. HNP1 derived from proHNP1A had microbicidal activity similar to that of native HNP1 (Fig. 4) . However, HNP1 derived from proHNP1B was devoid of staphylocidal activity (Fig. 4) . Thus, formation of native disulfide linkages in HNP1 is essential for the staphylocidal activity of the peptide, and may reflect a further requirement for dimerization.