The invention relates to a portable device for haemodialysis, comprising a haemodialyser (1) mounted to a blood circuit and connected at one of the dialysate connectors (7) thereof to a plastic tube (8) connected to a pump (9) which is itself connected to a reverse osmosis membrane in a cartridge or any other water extraction device (10) in turn connected at one of its two outlets to (i) a waste collection bag (11) and (ii) a reservoir (12) for osmosis-purified water, said reservoir being in turn connected to a pump (13) connected at its outlet to a second tube (16) connected to the other dialysate connector of the haemodialyser (15), thereby closing the circuit. Two reservoirs are mounted by means of solenoid valves (19, 20) on the tube (14) connecting the osmosis-purified water reservoir (12) and the pump (13), said reservoirs being filled with concentrated solutions of sodium bicarbonate and calcium chloride respectively (17, 18). During extra-renal purificaiton sessions, the device operates sequentially, under the control of a central unit (5), alternating two types of cycles. An isolated filtration cycle followed by a bicarbonate exchange cycle, and subsequently another isolated filtration cycle followed by a calcium chloride exchange cycle.Linvention concerne un dispositif portable pour hémodialyse qui comporte un hémodialyseur (1) monté sur un circuit sanguin et relié par lun de ses embouts dialysat (7) à un tuyau en plastique (8) relié à une pompe (9) qui est elle-même connectée à une membrane dosmose inverse conditionnée en cartouche ou tout autre dispositif dextraction deau (10) elle-même reliée au niveau de lune de ses deux sorties dune part à un sac pour le recueil du rejet (11) et dautre part à un réservoir deau osmosée (12) lui-même relié à une pompe (13) connectée à sa sortie à un second tuyau (16) connecté à lautre embout dialysat de lhémodialyseur (15) et qui ferme ainsi le circuit. Sur le tuyau (14) reliant le réservoir deau osmosée (12) à la pompe
