Abstract: A microsample device for blood sample collection comprises a hypodermic needle to which is attached a mixing chamber having an enlarged bore relative to the bore of its inlet and outlet conduits, and a supply of a soluble solid anticoagulant contained within the chamber. The anticoagulant is automatically mixed with the blood sample in the mixing chamber, eliminating the need for mixing balls or other mechanical mixing elements. The exit conduit from the mixing chamber leads to a capillary tube of sufficient length to accommodate a desired blood sample. The free end of the capillary tube is provided with a hydrophobic filter which permits air to escape from the interior of the collecting device as the blood sample enters but which blocks the further flow of blood as soon as the device is filled.