The present study outlines the relationship between cerebral and systemic hemodynamics in patients with septic shock. Sepsis is an immune mediated systemic disease in which the systemic vascular resistance (SVR) often decreases as a result of a Gram negative sepsis. The result is a hyperdynamic systemic circulation with redistribution phenomena in different organ systems. In order to study the effect of sepsis on cerebral vessels 20 patients with septic shock (12 men, 8 women, mean age 57.9 years) were subjected to both pulmonary artery catheter and transcranial Doppler (TCD) monitoring. The data were correlated to the APACHE II score and outcome. The study showed that cerebral mean and end-diastolic blood flow velocities (BFV) in the middle cerebral arteries significantly enhanced if the SVR-index decreases. In some patients a severely reduced SVRI (below 500 dynes.s/cm5.m2) was observed in combination with a downstroke latent steal phenomenon. TCD abnormalities were strongly related to disease severity and outcome. The increased BFV are explained by a mild vasospasm of the basal cerebral arteries. TCD appears to be a valuable tool to monitor the cerebral hemodynamics in these patients. They are particularly at risk for ischemic brain damage if they are subjected to therapeutic or spontaneous hyperventilation, which can potentially be detected by TCD.