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.