A device for taking samples of arterial blood with a view to its subsequent gasometric analysis comprises a main body forming a reservoir in which a free piston travels. Said piston isolates the blood from the air and cannot be manipulated by the operator. The device also includes a filter located at the end of the piston stroke which is permeable to air and impermeable to blood, allows the operator to observe the blood as it advances, and acts as a barrier to excessive blood flow, and a stopper which ulitmately seals the system and facilitates its tranport. In contrast to conventional invasive systems, this device, which does not need to be sterilized, makes it possible to obtain a blood sample which, after sampling, is only minimally contaminated with the ambient air, is available in a sufficient quantity, and is only slightly coagulable.