An assembly for handling medical fluids, e.g. for dialysis comprising a disposable cassette (10) with a rigid cassette base (12) inserted into the machine, is new. An assembly to handle a medical fluid, e.g. for dialysis, comprises a disposable cassette (10) with a rigid cassette base (12) inserted into the machine. The cassette has structured chambers and channels(28) with valves (30), covered by a film. The machine has actuators and sensors for the operation of the machine with the inserted cassette. The cassettes are provided in different integration formats for different applications, with blood flow channels (24,26).