Ticlopidine is an antiplatelet agent used as a drug to prevent the recurrence of cerebral infarction or ischemic heart disease. Close attention has recently been paid to the superiority of this drug to aspirin in the prevention of stroke. Its mechanism of action differs from aspirin, dipyridamole, and sulfinpyrazone. Inhibition of the adenosine diphosphate induced pathway of platelet aggregation, along with the activation of adenylate cyclase and suppression of platelet-activating factor and thromboxane A2, are the postulated mechanisms of action of ticlopidine. Because ticlopidine causes neutropenia and agranulocytosis in roughly 1% of treated patients, usually within the first 3 months of treatment, this drug has been reserved for patients intolerant to aspirin therapy. We reported two cases of ticlopidine-induced neutropenia and one patient hospitalized with severe neutropenia and pneumonia.