A new differential photoacoustic (PA) detector equipped with band-rejecting acoustic filters has been developed for diode laser photoacoustics. The differential design provides good flow and electric noise suppression. The detector was used for monitoring ammonia in continuous flow operation. The first test measurements of synthetic air-ammonia mixtures were carried out using a 5 mW distributed feedback (DFB) diode laser at 1.53 μm, providing a sensitivity limit of about 300 ppbV. Because of the adsorption of ammonia molecules on the walls of the detector and the gas tubing, high flow rates were needed for the measurements in the 1–100 ppmV concentration range. The smallest concentration detected was 1 ppmV.