The invention concerns a bag for a circuit of a biological liquid treatment installation, comprising two flexible films (65, 66) joined to each other and delimiting a zone (67) for treatment of said liquid according to a closed outline, connectors for liquid emerging on the inside and on the outside of at least one side of said outline and a network for conveying liquid between said connectors, said network having conduits which are formed between said flexible films and which extend in said zone for treatment when said bag is clamped between first shell and second shell of the circuit at least one first through aperture (73) on one side of said outline and which enables said bag to be positioned in said circuit and at least one second through aperture (75) in the treatment zone of said liquid, between conduits of the conveying network, enabling the passage of means for clamping said bag in said circuit.
