Abstract: A method non-dispersive infrared (NDIR) gas analysis, which can be carried out by a gas analyser comprising a cell (10) containing of gas, a sender (30) of IR waves and at least a receiver (40) of such waves. The transmission of IR waves and/or the reception of IR waves after the passage of the gas occur directly in the cell (10) same wherein the gas is fed. The analyser has a body (11) defining the cell (10), a sender (30) of IR waves and at least a receiver (40) of such waves, that are located opposite to each other with respect to the cell (10). The IR sender (30) and the receiver (40) are both arranged in the cell (10) at its end (13,14). The body (11) has inlet (15) and outlet (16) channels for the gas and a cavity (17), which can be metal coated inside and that defines the optical path (80) for the IR waves.