Abstract: For portable use of peritoneal dialysis, a flexible bag of plastic material has two chambers therein, one being a dialysis liquid chamber (42) and substantially larger than a further disinfectant chamber (8); the bag is formed of thermoplastic material, heat-sealed together at seam lines extending thereacross, and sealed into the seam lines are a communication line (16) from the dialysis chamber (42) to the outside, and a branch duct (17) extending from the disinfectant chamber to the communication duct; the respective ducts are closed off at the inside of the chambers, after filling, by releasable closures, such as a ball squeezed into the duct, or a frangible pin which can be broken off by flexing the bag, thus permitting removal of, respectively, dialysis fluid and disinfectant from the respective chambers; used dialysis fluid can be returned into the bag.