Administration set adapted for adding a beneficial agent and with self-priming ability.

The administration set includes a receptacle (42) for receiving a cartridge containing a beneficial agent, whereby the agent can be entrained in fluid flowing through the receptacle (42). An air flask (46) is mounted downstream of the receptacle and includes an air chamber (58) whose cross-sectional area is greater than that of the fluid conduit (28) joining the receptacle (42) to the air flask (46). The chamber has an inlet (48) at an upper end and an outlet (50) at a lower end. Liquid entering the air flask drops to the outlet and air is retained between a layer of liquid above the outlet in the chamber. A sterile barrier (62) may be provided between the inlet and the outlet.