Method for the preparation of at least one compound from blood, in which an extraction device is used comprising a casing , a first needle projecting from the casing , a second needle projecting into a housing area of the casing , a switch-unit operable to open and close the passage of material from the first needle to the second needle , and a user-operable button that projects from the casing for operating the switch-unit to open and close the passage of material from the first needle to the second needle , characterised in that the method comprises the steps of: i) providing blood in a sealed, first container with a pressure below atmospheric pressure, the first container containing at least one anticoagulant; ii) separating the blood in said first container, by centrifuging the first container, into at least the following fractions: a fraction of red blood cells in the bottom part of the first container, a fraction of white blood cells and platelets above the preceding one and, above, a plasma fraction with a platelet gradient concentration, said gradient decreasing towards the top part of the first container; iii) inserting the first needle of the extraction device substantially up to the top level of the highest fraction contained in the first container; iv) receiving a second container, which is vacuum-sealed and has a pressure below that of the first container, in the housing area of the extraction device and connecting the second container to the second needle of the extraction device; v) pressing the user-operable button and waiting for a certain period of time until a required amount of plasma, white blood cells and platelets and/or red blood cells is/are transferred, as a result of the difference in pressures, to the second container; vi) removing the second container from the extraction device; vii) adjusting the degree to which the first needle is introduced so that it once again reaches the top level of the remaining fractions, and repeating steps iv to vi. i) providing blood in a sealed, first container with a pressure below atmospheric pressure, the first container containing at least one anticoagulant; ii) separating the blood in said first container, by centrifuging the first container, into at least the following fractions: a fraction of red blood cells in the bottom part of the first container, a fraction of white blood cells and platelets above the preceding one and, above, a plasma fraction with a platelet gradient concentration, said gradient decreasing towards the top part of the first container; iii) inserting the first needle of the extraction device substantially up to the top level of the highest fraction contained in the first container; iv) receiving a second container, which is vacuum-sealed and has a pressure below that of the first container, in the housing area of the extraction device and connecting the second container to the second needle of the extraction device; v) pressing the user-operable button and waiting for a certain period of time until a required amount of plasma, white blood cells and platelets and/or red blood cells is/are transferred, as a result of the difference in pressures, to the second container; vi) removing the second container from the extraction device; vii) adjusting the degree to which the first needle is introduced so that it once again reaches the top level of the remaining fractions, and repeating steps iv to vi. <EOS>