A machine for injecting fluids into meat or fish products includes an injection head with parallel hollow needles that can be retracted by a contrast elastic device, provided to be lifted and lowered in relation to a conveyor for conveying products, each needle having an inlet opening leading into its cannula that can be located in a pressurized fluid injection chamber having a fluid inlet, the chamber being formed by a block with longitudinal ducts interconnected by ducts and a plurality of transverse ducts for the passage of the needles intersecting the longitudinal ducts, each duct including sleeves provided with seals, the block being detachable from a housing for the head and fixed by oscillating plates, one for guiding the needles and the other carrying a plurality of cylinders supplying the contrast elastic device.