Thrombotic thrombocytopenic purpura (TTP) has a high mortality rate if left untreated with plasma exchange promptly. We report two cases of ticlopidine-induced TTP, which lesser dosages of ticlopidine (200-250 mg/day) were prescribed and were treated with plasma exchange (PE) plus steroids. The first case was treated successfully, but the second case did not respond to our treatment and died of a progressive disease complicated with pneumonia. In sum, we recommend careful use of ticlopidine, regardless of the dosages prescribe and regardless of how long the drug is used. Moreover, the adverse effect of ticlopidine should be closely monitored.