Abstract: The invention relates to means for extracting products to be analysed. Said means comprise a device for extracting one or more layers comprising the sought-after products or constituents from a test tube (1) containing numerous different adjacent or overlapping layers in a liquid medium forming a continuous or discontinuous density gradient (2). Said invention is characterised in that it comprises: a standard test tube (1), an extraction capillary or tube (3), which can be pre-positioned according to the layer to be extracted, and means for obtaining a laminar flow of one or more layers from the tube without suction, either by applying overpressure to the top of the liquid medium with a low-density liquid, gas or fluid or by exerting a centrifugal force. The invention can be used to extract one or more layers of constituents, for example, from a blood mixture.