During a single blind study the influence of hypervolemic hemodilution (Infusion of 500 cc Elohäst 6%) on micro- and macrocirculation, transcutaneous pO2 and fluidity of blood of apparently healthy subjects was investigated. Blood pressure and heart rate remained unchanged during and after the infusion. One hour after the infusion there was a significant increase in the blood flow of the common carotid artery and the cutaneous circulation, and after 3 h a significant increase in conjunctival oxygen partial pressure was observed. The decrease in hematocrit was significant at all measuring points but most marked after 3 h (with 4.2 by volume). After 3 h and 6 h a significant increase in plasma viscosity and erythrocyte aggregation could be observed, whereas both parameters were unchanged during the early phase.