The effect on cryoprecipitate factor VIII recovery of three imortant variables has been investigated. The design of the study was such as to eliminate, for the purpose of internal comparisons, spurious effects such as those due to the variation in factor VIII levels in donor plasma. The choice of anticoagulant was shown to be of particular significance, plasma collected into CPD anticoagulant giving higher cryoprecipitate factor VIII yield thoughout the study. The effect on cryoprecipitate factor VIII recovery of delay before separation and freezing of the plasma was more complex. Very fresh plasma (separated and frozen within 2 h of collection) gave the highest recovery of factor VIII, but no difference was detected between cryoprecipitate factor VIII recovery of plasma separated and frozen at 4 h and at 18 h after blood collection. Controlled rapid thawing of the plasma was also shown to be advantageous, at least for the preparation of cryoprecipitates from plasma anticoagulated with CPD anticoagulant.