A procedure for preparing single units of freeze-dried cryoprecipitate (cryo) in the original bags is described in detail. Batches of frozen plasma bags were rapidly thawed by rocking in a water bath, centrifuged and after complete removal of supernate the compact cryo pellets (2-5 g) were lyophilized with the aid of a holding tray with a filtered air chamber designed for this purpose. Adding synthetic amino acids has greatly improved stability of the dried concentrate during storage and has increased its resistance to heat denaturation (e.g. less than 10% loss of potency after 20 h at 70 degrees C). The method is presented as a viable option for safe and economical manufacture of a stable factor VIII concentrate.