Leukocytes may have an important role in the pathogenesis of brain injury after ischemia. Expression of adhesion molecules on leukocytes and/or endothelia is needed for leukocytes to adhere to endothelia and infiltrate into the injured brain. The purpose of the present pilot study is to delineate whether the expression of leukocyte adhesion molecules, CD11a and CD18, are upregulated in patients with ischemic stroke and transient ischemic attack. Ten patients with ischemic stroke, 6 with transient ischemic attack (TIA), and 11 age and risk factor matched controls were studied. Using immunofluorescence phenotyping and flow cytometry, leukocyte membrane expression of CD11a and CD18 were measured within 72 h after onset of ischemia. Follow-up measurements were performed at 5-7 days after ictus in 6 patients with stroke, and at 3-5 days after ictus in 3 patients with TIA. CD11a immunofluorescence (IF) was significantly increased within 72 h after onset of symptoms in patients with stroke as well as TIA compared with the control group (p < 0.017). IF of CD18 also increased in both patient groups, but significance was reached only in the TIA group (p < 0.05). No difference of CD11a and CD18 IF was detected between stroke and TIA groups. Follow-up measurement of CD11a and CD18 showed a trend of decrease, but CD11a IF remained significantly elevated compared with the control group (p < 0.017). Expression of leukocyte adhesion molecules CD11a, and CD18 are upregulated in patients with ischemic stroke and TIA. Although these data are preliminary, our data suggest that these molecules are associated with cerebrovascular disorders including ischemic stroke and TIA.