10 patients with ischemic cerebral lesions were treated with 1,200–1,500 mg parenteral pentoxifylline daily for 10 days. The following rheological parameters were determined before treatment and every third day after the start of treatment: erythrocyte deformability and aggregation, hematocrit, plasma viscosity and yield shear stress. 2 patients were submitted to isovolemic hemodilution. Among all rheological parameters, the erythrocyte deformability and the yield shear stress improved significantly, whereas plasma viscosity and erythrocyte aggregation did not change. 1 patient died 20 days after admission. 9 patients improved clinically. Because of the small number of patients correlations between clinical outcome and therapy are not possible.