Abstract: The invention relates to a device for the equilibrium dialysis of fluids having small volumes. The object of the invention of creating a device for equilibrium dialysis , the device being designed as a simple as possible, being universally usable and reliable in the use thereof, with which a large ratio of the membrane surface to the sample volume is created and which facilitates very short diffusion paths inside the sample as well as low sample losses, even with small sample volumes, is achieved in that a device is proposed, which comprises corresponding capillaries (1, 1?), which are connected through a membrane (2) and each are open at the ends on both sides, said capillaries for dialysis purposes each comprising a preferably substantially U-shaped arched capillary portion, and the at least one opening (4, 4?) thereof being provided each with a sealing element for introducing and/or removing the liquid.