the present invention describes a method of preventing neutrophil chemotaxis , either in vitro or at a biological site using peptides whose amino acid sequence is derived at least in part from the sequence of native neutrophil activating factor . the peptides do not have measurable chemotactic activity against human neutrophils , but they are antagonistic to native naf . the method of preventing neutrophil chemotaxis is practiced by adding sufficient amounts of the claimed peptides to neutrophils in a biological fluid or appropriate medium to inhibit neutrophil chemotaxis . the claimed peptides may have therapeutic value in patients with adult respiratory distress syndrome or with other inflammatory lesions known or found to be caused by naf .