A method for the large-scale preparation of a coagulation factor IX concentrate from human plasma is described. The method includes absorption of the coagulation factors from cryosupernatant plasma onto DEAE-Sephadex, extensive washing of the gel and elution of the coagulation factors with 0.5 M phosphate buffer at 6.85, followed by desalting of the eluate in a column of Sephadex G-25, then by lyophilization, dissolving and sterile filtration, and finally by freeze-drying of the final product. Experiments performed with HBsAg-positive plasma demonstrated a decrease in the HBsAg content by a factor of 10^-5 during the process. The product is inactive in Na-PTT assay. The process yields an about 100-fold purified factor IX concentrate containing also factors II,VII, and X, but in relatively smaller amounts. The average yield relative to factor IX is 60%. The batch size has been from 16 to 150 litres of plasma and about 300 batches of the concentrate have been prepared. About 5,100 bottles (about 4.0 x 10^6 U of factor IX) of the concentrate have been used in the treatment of patients with haemophilia B. The clinical effect has always been good and the in vivo response to factor IX was 1.15±0.30%/U/kg body weight. Two cases of HBsAg-negative hepatitis that may have been caused by the concentrate, were detected. No thrombotic complications were found.