A delivery assembly for a machine for preparing liquid products by means of cartridges that have a substantially cup-shaped body, which houses an amount of at least one substance capable of forming a liquid product through water and/or steam, the delivery assembly having a substantially horizontal axis and including: - an inlet passage, to enable insertion of a cartridge into the delivery assembly; - an injector device, designed to introduce into the cartridge water and/or steam under pressure; - an infusion chamber, facing the injector device and capable to receive one said cartridge; - retention means (42, 47), capable of maintaining the cartridge in a position substantially coaxial to the infusion chamber and to the injector device; - an actuation system, designed to cause relative displacements between the injector device and the infusion chamber, between a spaced position and a close position, the infusion chamber being in a fixed position with respect to a stationary structure of the delivery assembly and the injector device being mounted displaceable with respect to the infusion chamber and to said stationary structure, wherein the retention means (42, 47) are capable of assuming a retention position, in which the cartridge is retained in said position substantially coaxial to the infusion chamber and to the injector device, and a release position, in which the cartridge is free to fall towards an outlet passage of the delivery assembly, the retention means (42, 47) being switchable from said retention position to said release position by means of a mechanical interaction or interference thereof with respect to fixed elements of said stationary structure of the delivery assembly, wherein the retention means (42, 47) comprise a lower support element designed to support the cartridge from beneath, the support element being sustained in a displaceable way by the injector device in a part thereof that generally faces the outlet passage, the support element being switchable from said retention position to said release position in the course of the displacement of the injector device towards said close position, the delivery assembly being characterized in that the support element is mounted on a body of the injector device for being displaceable between a forward position and a withdrawn position, to which the respective retention and release positions correspond, respectively, and in that the support element is capable of interfering mechanically with a first stop element and a second stop element, in such a way that the passage from said forward position to said withdrawn position is caused by the mechanical interference of a generally front region of the support element with the first stop element, in the course of an approaching movement of the injector device towards the infusion chamber, and the passage from said withdrawn position to said forward position is caused by the mechanical interference of a generally rear region of the support element with the second stop element, in the course of a movement of the injector device away from the infusion chamber. - an inlet passage, to enable insertion of a cartridge into the delivery assembly; - an injector device, designed to introduce into the cartridge water and/or steam under pressure; - an infusion chamber, facing the injector device and capable to receive one said cartridge; - retention means (42, 47), capable of maintaining the cartridge in a position substantially coaxial to the infusion chamber and to the injector device; - an actuation system, designed to cause relative displacements between the injector device and the infusion chamber, between a spaced position and a close position, the infusion chamber being in a fixed position with respect to a stationary structure of the delivery assembly and the injector device being mounted displaceable with respect to the infusion chamber and to said stationary structure,