Gas analyser for measuring the concentration of a gas component in a measurement gas based on the method of wavelength modulation spectroscopy, having - a wavelength-tunable light source, - a first modulation device which periodically varies the wavelength of the light from the light source by way of an absorption line of interest of the gas component and thereby additionally modulates it with a frequency (f 0), - means which guide the light from the light source through the measurement gas to a measurement detector or guide a first part of the light from the light source through the measurement gas to the measurement detector and guide a second part of the light to a reference detector through a reference gas containing the gas component to be measured in a predetermined concentration, - an evaluation device (13, 14, 23) which demodulates and evaluates a measurement signal generated by the measurement detector, or the measurement signal and a reference signal generated by the reference detector in the case of a harmonic component (n·f 0) of the frequency (f 0), and - a second modulation device which modulates the wavelength of the light from the light source with the harmonic component (n·f 0) and a modulation intensity which is controlled as a function of an output signal of a detector demodulated in the case of the harmonic component (n·f 0), characterised in that - the modulation intensity is controlled as a function of the demodulated output signal of the detector, which is the measurement detector or the reference detector, - an arithmetic unit is present which, in a model based on an analytical approximation description of the Lorentz-shaped absorption line of the gas component to be measured and with the aid of additional information from the current demodulated reference signal, generates a model signal for the demodulated measurement signal or reference signal, forms a difference signal between the model signal and the demodulated measurement signal or reference signal, and controls the modulation intensity with the difference signal. - a wavelength-tunable light source, - a first modulation device which periodically varies the wavelength of the light from the light source by way of an absorption line of interest of the gas component and thereby additionally modulates it with a frequency (f 0), - means which guide the light from the light source through the measurement gas to a measurement detector or guide a first part of the light from the light source through the measurement gas to the measurement detector and guide a second part of the light to a reference detector through a reference gas containing the gas component to be measured in a predetermined concentration, - an evaluation device (13, 14, 23) which demodulates and evaluates a measurement signal generated by the measurement detector, or the measurement signal and a reference signal generated by the reference detector in the case of a harmonic component (n·f 0) of the frequency (f 0), and - a second modulation device which modulates the wavelength of the light from the light source with the harmonic component (n·f 0) and a modulation intensity which is controlled as a function of an output signal of a detector demodulated in the case of the harmonic component (n·f 0), - the modulation intensity is controlled as a function of the demodulated output signal of the detector, which is the measurement detector or the reference detector, - an arithmetic unit is present which, in a model based on an analytical approximation description of the Lorentz-shaped absorption line of the gas component to be measured and with the aid of additional information from the current demodulated reference signal, generates a model signal for the demodulated measurement signal or reference signal, forms a difference signal between the model signal and the demodulated measurement signal or reference signal, and controls the modulation intensity with the difference signal.