The absorption of factor VIII from gel filtration fractions, concentrates and plasma by aluminium hydroxide has been studied. Significant quantities of factor VIII could be removed when the protein concentration was low; the percentage absorbed increased with decreasing initial protein concentration. Factor VIII R:Ag and VIII:C were removed in parallel, but absorption of a high purity concentrate resulted in selective absorption of the lower molecular weight forms of factor VIII. Elution of the absorbed proteins gave a poor yield of VIII R:Ag, with no detectable VIII:C. Absorption of plasma showed no detectable loss of VIII R:Ag, but an apparent decrease of VIII:C of about 10%.