For the assessment of peripheral blood leukocyte chemotaxis dysfunction in rapidly progressive periodontitis, peripheral blood leukocyte of 13 patients were isolated, and tested by the method of blind well chamber technique which was recently developed by Park. Data analysis was performed from the speed of cell migration from the bottom of filter paper to the top for 18 minutes at the condition of chemo-attractant(Zymosan-activated serum). Eight of the 13 patients (62%) exhibited statistically significant inhibition of leukocyte chemotaxis, 4 patients revealed normal function and the other one patients showed elevated leukocyte chemotaxis. Four of the 8 patients in chemotaxis dysfunction showed significant inhibition of random migration and chemotaxis dysfunction both. Two of these 4 patients exhibited random migration impairment, elevation of C.D.I. and chemotaxis dysfunction. The results indicated that the progression of rapidly progressive periodontitis was influenced by the leukocyte chemotaxis dysfunction, and half of these dysfunction was associated with cell-defect of leukocyte.