An air injection system for a hydro-massaging bath is described. An air convecting conduit is in communication with a plurality of injecting orifices formed in a peripheral wall of the bath. An air blower injects air under pressure in an entry opening of the air convecting conduit. A water spray injector is located downstream of the entry opening and upstream of the air injecting orifices to inject a spray of a predetermined volume of water in the injected air under pressure. A water supply conduit is connected to the water spray injector and has a flow regulating valve to regulate the volume of water spray injected in the heated air to saturate the air with water. A shut-off valve is provided in the water supply conduit, and a heater is disposed in the air convecting conduit downstream of the water spray injector and upstream of the air injecting orifices wherein heated, humidified air injected in the water contained within the bathtub does not produce a cool sensation on the body of a user person.