Forty patients (age 67 +/- 9 years) with acute central artery obstruction (CAO; n = 20) or branch artery occlusion (BAO; n = 20) of the retina were examined in a prospective study. All patients received a hypervolemic or isovolemic hemodilution, depending on their hematocrit values, for a period of ten days. Clinical, hemodynamic, and rheological data of these patients were recorded before therapy, after ten days, and after six weeks. Under this therapy the central vision of 24 patients (CAO: n = 10; BAO: n = 14) improved by two or more stages. The extent of the circulatory disturbance was determined by arteriovenous passage time and dye bolus velocity. Compared with a control group, a significantly increased arteriovenous passage time and decreased dye bolus velocity were observed initially. The values after ten days of therapy and after six weeks were significantly improved (P less than 0.01) as compared to the initial values. Patients with longer latency showed almost normal retinal hemodynamics, even without therapy, after some weeks. However, in most cases the spontaneous improvement occurred too late. Therefore, it appears important to achieve early reperfusion by therapy.