Date expired commercial F.VIII concentrates (1.000 I.U. in 15 ml) were chromatographed through a Sepharose 4B in Tris-HCI (0.15 M, pH = 7.4) column. The void volume of this column was found to constitute an enriched vWF preparation. Half a milliliter of this preparation (protein content: 200 micrograms/ml) was mixed (1: 3) with Freund's complete adyuvant and administered to two rabbits by intramuscular route. A total of 3 doses were administered at days 1, 15 and 21 and the 2 animals were bled at day 30. The serum samples so obtained were pooled and analysed (DGD and IEP) for anti-vWF and anti-NHP activity. Strong anti-vWF specificity could be demosntrated. However, since a weak anti-fibrinogen and anti-IgG contaminant activity was also detected, the pool was filtered through a column containing normal human plasma coupled to a periodate activated Sephacryl S-1.000 immunoadsorbent. The filtrate, which was found to contain only a strong anti-vWF activity, was again processed by affinity chromatography through another Sephacryl immunoadsorbent containing a commercial F.VIII concentrate of the same lot employed for purifying the vWF. The eluate so obtained demonstrated to be constituted only by a pure rabbit IgG with strong anti-vWF specificity and was completely devoid of activity against any other human plasmastic protein. The method was found to be rapid, simple and economic, yielding as much as 5 mg of specific IgG for every 10 ml of antiserum so processed.