The properties of polymorphonuclear leukocytes [PMNL] isolated from a patient with meningococcal meningitis were reported. No differences in phagocytic capacity and random locomotion between the patient''s polymorphonuclear leukocytes and normal PMNL were found, but by using activated normal human serum as chemo-attractant it was found that PMNL isolated from the CSF had lost their ability to respond chemotactically. The deactivation was found to be accompanied by surface property changes of the cells.