During 4 hours, in-vitro hemoperfusion of human blood was performed in 4 series of experiments: control, cellulose coated charcoal, polyacrylohydrogel coated charcoal and uncoated charcoal. In the control series little change on corpuscular elements and electrolytes was observed. In all hemoperfusion series there was little change of RBC and uniformly a marked fall of the granulocyte count. Platelet- and lymphocyte counts were significantly less affected by cellulose coated charcoal than by the other preparations. Coated and uncoated charcoal absorbed avidly calcium and glucose from the blood. By contrast the potassium level decreased moderately with polyacrylohydrogel coated and uncoated charcoal, whereas the opposite was observed with cellulose coated charcoal.