A hemodialysis system for use with any type of dialyzer, such as coil-type, Kiil-type and capillary-type or hollow fiber-type dialyzers, which has a fluid circulation circuit and a bypass circuit short-circuiting the fluid circulation circuit. At one junction between the fluid circulation circuit and the bypass circuit, an ejector is employed. The ejector has a nozzle, a diffuser axially aligned with the nozzle and defining an orifice and a suction chamber communicated with the orifice. During circulation of the dialysate in the circulation circuit and from the nozzle onto the diffuser of the ejector, a negative gauge pressure is developed in the suction chamber so that the dialysate can be drawn through the bypass circuit. The circulation circuit and the bypass circuit have respective coupling assemblies for removable connection with the coil-type dialyzer and with the Kiil-type or capillary-type, or hollow fiber-type, dialyzer.