There is an increased prevalence of blood hyperviscosity in patients with arterial hypertension, and viscosity changes are related to hypertensive organ damage such as e.g. left ventricular hypertrophy. Various indices of hemorheology may be assessed in studies of hypertensive patients, most commonly viscosity, erythrocyte filtration, erythrocyte aggregation, platelet aggregation, etc. In vitro assessment of erythrocyte deformability and adrenaline induced platelet aggregation was performed after urapidil administration. Increasing concentrations of urapidil (25-150 microM) caused a dose dependent improvement of the erythrocyte rigidity index as well as inhibited adrenaline induced platelet aggregation. The beneficial effects of urapidil on hemorheology could add to its therapeutic effects in the treatment of arterial hypertension.