A system for sampling, preparing, and fractioned dispensing of samples of a fluid, in particular blood, comprising: • a sample-taker member, in particular a needle, having an end suitable for piercing a stopper of a tube containing a fluid, and at least one orifice suitable for enabling air to be delivered to said tube and for sucking up a sample of fluid in the tube; • at least one means for sucking up and delivering the sample of fluid, said means being connected to the sample-taker member; • at least one preparation and dispensing device comprising: guide means constituted by a channel which is adapted to receive the sample-taker member and for guiding it in translation within the device along an axis YY' through the channel until the end of the sample-taker member is introduced into the tube containing the fluid; at least one preparation chamber (4, 5) enabling an aliquot of a sample of fluid dispensed in the chamber by said sample-taker member to be prepared in a stream of an appropriate reagent, the guide means passing through the preparation chamber (4, 5) and communicating therewith in such a manner as to enable a said aliquot of a said fluid sample to be dispensed into the chamber by the sample-taker member in a determined position thereof within the guide means, the preparation chamber (4, 5) including an introduction orifice (4a, 5a) for introducing at least one reagent (R1, R2) into the chamber for mixing the reagent with a said aliquot, and at least one dispensing orifice (4b, 5b) for dispensing the mixture formed by said aliquot and said reagent to recovery and/or analysis means (21, 22); • at least one means (17, 18, 19, 20) for dispensing selected volumes of at least one reagent fluid, said means being connected to the introduction orifice (4a, 5a) of at least one preparation chamber (4, 5) of the preparation and dispensing device; and • at least one means (21, 22) for receiving and/or analyzing a mixture of an aliquot (a1, a2) of the sample of fluid and a determined volume of reagent, said means being connected to the dispensing orifice (4b, 5b) of the preparation chamber (4, 5) of the preparation and dispensing device. • a sample-taker member, in particular a needle, having an end suitable for piercing a stopper of a tube containing a fluid, and at least one orifice suitable for enabling air to be delivered to said tube and for sucking up a sample of fluid in the tube; • at least one means for sucking up and delivering the sample of fluid, said means being connected to the sample-taker member; • at least one preparation and dispensing device comprising: guide means constituted by a channel which is adapted to receive the sample-taker member and for guiding it in translation within the device along an axis YY' through the channel until the end of the sample-taker member is introduced into the tube containing the fluid; at least one preparation chamber (4, 5) enabling an aliquot of a sample of fluid dispensed in the chamber by said sample-taker member to be prepared in a stream of an appropriate reagent, the guide means passing through the preparation chamber (4, 5) and communicating therewith in such a manner as to enable a said aliquot of a said fluid sample to be dispensed into the chamber by the sample-taker member in a determined position thereof within the guide means, the preparation chamber (4, 5) including an introduction orifice (4a, 5a) for introducing at least one reagent (R1, R2) into the chamber for mixing the reagent with a said aliquot, and at least one dispensing orifice (4b, 5b) for dispensing the mixture formed by said aliquot and said reagent to recovery and/or analysis means (21, 22); guide means constituted by a channel which is adapted to receive the sample-taker member and for guiding it in translation within the device along an axis YY' through the channel until the end of the sample-taker member is introduced into the tube containing the fluid; at least one preparation chamber (4, 5) enabling an aliquot of a sample of fluid dispensed in the chamber by said sample-taker member to be prepared in a stream of an appropriate reagent, the guide means passing through the preparation chamber (4, 5) and communicating therewith in such a manner as to enable a said aliquot of a said fluid sample to be dispensed into the chamber by the sample-taker member in a determined position thereof within the guide means, the preparation chamber (4, 5) including an introduction orifice (4a, 5a) for introducing at least one reagent (R1, R2) into the chamber for mixing the reagent with a said aliquot, and at least one dispensing orifice (4b, 5b) for dispensing the mixture formed by said aliquot and said reagent to recovery and/or analysis means (21, 22); • at least one means (17, 18, 19, 20) for dispensing selected volumes of at least one reagent fluid, said means being connected to the introduction orifice (4a, 5a) of at least one preparation chamber (4, 5) of the preparation and dispensing device; and • at least one means (21, 22) for receiving and/or analyzing a mixture of an aliquot (a1, a2) of the sample of fluid and a determined volume of reagent, said means being connected to the dispensing orifice (4b, 5b) of the preparation chamber (4, 5) of the preparation and dispensing device.