A complete neurological and laboratory assessment was made of 31 transient ischemic attack (TIA) and 33 acute ischemic stroke patients. Laboratory parameters were compared with 33 age- and sex-matched controls. Erythrocyte deformability was characterised by determining the relative cell transit time (RCTT) with a St. George filtrometer. Plasma viscosity was measured with a Haake microviscosimeter. In comparison with controls, fibrinogen content, erythrocyte sedimentation rate (ESR), platelet and leukocyte count, erythrocyte RCTT and plasma viscosity were found to be significantly higher in stroke patients. In TIA patients the elevation of these values was not significant with the exception of platelet count. Our results suggest that the hemorheological alterations observed in TIA and stroke are largely non-specific findings and associated with the atherosclerotic disease of patients. The significant elevation of leukocytes, fibrinogen and plasma viscosity in acute stroke versus TIA probably reflects the systemic acute phase response of organism to cerebral infarction.