A procedure is described for the preparation of a concentrate of factors II, VII, IX and X, using a modification of the method of Bruning and Loeliger, involving aluminium hydroxide adsorption of ACD plasma followed by phosphate elution and dialysis. The concentrate produced had an average factor IX activity of 7.4 U/ml with a yield of 61% and a purification of 34.5. Clinical trials in patients with either a congenital deficiency of factor IX or liver disease showed that the concentrate was well tolerated and was an effective haemostatic agent. The average factor IX response was 1.09% for each U/kg injected, giving a recovery of 48%.