The role of neutrophils in psoriasis has long been discussed. We report a patient with long-standing psoriasis vulgaris who showed rapid improvement during agranulocytosis caused by ticlopidine. The patient did not develop any new psoriatic lesions for several days, although neutrophils increased daily after the administration of ticlopidine was stopped. The day after the peripheral blood neutrophil count recovered, several psoriatic plaques reappeared. The correlation of psoriatic activity with peripheral blood neutrophil counts suggests that a certain number of neutrophils may be required to initiate and maintain psoriasis.