The polymorphonuclear neutrophil (PMN) chemotaxis index and modulation of serum factors in 15 Brazilian periodontal patients (five localized juvenile and ten adult periodontitis) and ten healthy subjects were examined. Adult periodontitis patients showed a normal chemotaxis index, Localized juvenile periodontitis LJP patients showed diminished chemotaxis and serum cell-directed inhibitor activity. The results suggest that PMN abnormalities could not be caused by only the neutrophils themselves, but also by modulation of serum factors acting on this LJP disease.