Abstract: In a method of preparing a plasma sample, blood from a donor is placed in the inner of two concentric tubes which are releasably connected together. The outer sample tube is labelled with data relating to the blood sample. After the concentric sample tubes have been centrifuged to separate out plasma from the blood, the outer tube is disconnected from the inner tube so that plasma can be poured into the outer tube. The outer tube, which carries the label, is then retained for analysis. As an alternative to centrifuging, a leakage path which is permeable to plasma but not blood cells can be provided at the base of the inner tube and plasma forced into the outer tube by application of external pressure.