A by-product of the preparation of platelet concentrates, by recently proposed methods, is fresh citrate-plasma at pH 6.5. Because this plasma might be a useful source of Factor VIII, the activity was investigated. Compared to unaltered citrate-plasma, the activity was found to be 54 per cent. However, after incubation with washed fresh erythrocytes the "acidified" plasma had the same Factor VIII activity as the control.

This suggests that, after infusion, pH 6.5 plasma is probably as effective a source of Factor VIII as ordinary ACD-plasma. This conclusion was supported by observations on Factor VIII concentrates prepared by cryoprecipitation. In such preparations additional ACD and pH are eliminated as factors in the assay system. Factor VIII concentration in the precipitates prepared from acidified plasma was found to be as high as in precipitates prepared from untreated plasma.

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