Abstract. A quantitative analysis was performed of the method of plasma fractionation used in our institute, a modified Cohn VI system, in order to develop and evaluate methods for the increment of antibody yield and quality of the immunoglobulin concentrate. For this purpose the distribution of the immunoglobulins IgG, IgM, IgA, the subclasses of IgG and several specific antibodies in the different fractions was analysed. In addition, the distribution of some plasma proteins which may be of importance for the quality of the immunoglobulin concentrate, such as α2M, α1‐antitrypsin, α2‐lipoprotein and fibrinogen, was determined. The average yield of IgG of immunoglobulin concentrates prepared from 31 plasma batches was 58% (SD 9%). Loss of IgG predominantly occurred in fraction III with an average of 25% (9 batches). Most of the measured antibody activities were similar to that of IgG. The anti‐D antibody showed a lower yield, the mean value of 13 batches was 41 % (SD 11 %), which could be attributed to a higher loss in fractions I and III. The steps in the ethanol fractionation in which considerable losses occurred, were analysed in order to improve the yield of immunoglobulins, especially of anti‐D. Suggestions for modifications leading to improvement of the yield are given.

Abstract. It was observed that during the preparation of normal anti‐D immunoglobulin concentrates by a modified Cohn VI method a considerable loss of anti‐D activity occurred in fraction III. A method was developed to prepare anti‐D immunoglobulin concentrates from fraction III by ethanol fractionation. Three batches were treated on a production scale. An average of 18% of the amount of anti‐D activity present in the original plasma, was recovered, which increased the total yield of anti‐D activity from 44 to 62%. The specific activity of anti‐D in the concentrate thus prepared was 2–3 times higher than that in the normal anti‐D immunoglobulin concentrate. The anti‐D immunoglobulin concentrate prepared from fraction III was diluted with normal immunoglobulin concentrate to reach an anti‐D concentration of 110–120 μg/ml. Using several analytical procedures no essential differences could be demonstrated between this final product and the normal immunoglobulin concentrate. After 8 months of storage at 4°C no significant decrease in anti‐D activity could be demonstrated.