This double-blind pilot study observed the effects of a twenty-one day oral ticlopidine treatment (250 mg/twice daily) on the neurologic outcome and the hemorheologic pattern of 15 patients and 15 placebo-treated controls. Patients and controls (age range sixty-six to eighty-six years) were included in the study within twelve hours of the onset of ischemic stroke, confirmed clinically and by computerized tomography. Scores on Hachinski's Scale and the following hemorheologic parameters were monitored weekly for twenty-one days: fibrinogen levels, the whole blood, unfractionated white and red blood cell filterability rates (through 5-micron-pore-diameter filters using a constant-flow positive-pressure system), and the leukocyte count and activation (by microscopic observation). The results showed treatment with ticlopidine improved the neurologic outcome (Hachinski's Score +36%, p less than 0.03) slightly but significantly (p less than 0.001) increased the average values of the whole blood (+19%) and red cell (+17%) filterability rates and decreased fibrinogen levels (-17%).