The invention relates to a sampling valve and to a device equipped with such a valve notably allowing haematogy Ineasttrenreaat to be taken from a blood sample. The valve comprise two external parts, one internal part clamped between said exterrtal parts, and means for regulating the relative angular position of these parts about to axis of rotation. The mienial part has opposite surfaces pressing in a sealed and sliding manner against adjacent surfaces of the external parts. The external parts comprise orifices, loops and ducts, said loops and said ducts being arranged in such a way as to communicate selectively with orifices passing through the internal part. The valve parts have no aliquot return groove or recess or labyrinth, thereby eliminating regions of turbulence. The valve is characterized in that two of the parts are able to rotate about the axis of rotation with respect to one of the said pans which is stationary, the rotary parts preferably being the external parts. The sampling valve also makes it possible to form calibrated volumes of a sample taken in the loops and/or the orifices of the internal pan.