Abstract.The influence of different variables on the yield of factor VIII in cryoprecipitate as prepared in the Central Laboratory of the Netherlands Red Cross Blood Transfusion Service, was studied. The following conclusions may be drawn:1In case blood should be stored, the use of the anticoagulant solution acid citrate dextrose (ACD) is preferable to citrate phosphate dextrose (CPD) or trisodium citrate (TSC).2The temperature of stored whole blood should not decrease below 8 °C because of a spontaneous precipitation of factor VIII from blood (and plasma) below this temperature.3Cryoprecipitate derived from rapidly frozen plasma (1 min) contains a decreased amount of proteins in comparison with cryoprecipitate prepared from slowly frozen plasma (45 min to 4 h). On the other hand, equal amounts of factor VIII activity were obtained in the precipitate after freezing of plasma at varying rates.4Rapid thawing of plasma results in both higher yields of factor VIII procoagulant activity and a higher specific activity of this factor in the resulting cryoprecipitate.5The sedimentation of cryoprecipitate is completed after 5 min centrifugation at 1,500 g.6At temperatures higher than 8 °C, cryoprecipitated factor VIII starts dissolving into the supernatant plasma or in buffer.7Factor VIII in lyophilized cryoprecipitate is stable at room temperature. At devated temperatures it rapidly looses its activity.8Evidence was obtained that the improvements which are introduced in the preparation of factor VIII do not lead to a product which is less stablein vitroas well asin viv