Refractory cases of periodontitis were assayed for chemotaxis of polymorphonuclear neutrophilic leukocytes using an in vivo assay. 9 refractory patients and 9 normal patients were studied. When cell counts were plotted against time, normal patients showed a single peak at 25-30 min after casein (chemo-attractant) challenge, whereas refractory patients showed 2 and 3 peaks of PMN's at varying time intervals. 5 of the refractory patients showed this pattern in tests of normal sulci as well as deep periodontal pockets. 4 of the refractory cases showed a double peak in tests of deep periodontal pockets. This suggests that some refractory cases have an intrinsic chemotactic defect of polymorphonuclear neutrophils while in others the defect may be a secondary phenomenon. It appears that patients with refractory periodontitis have the characteristic cell response that was reported for LJP.