In this work we present the quantitative and qualitative detection of organic vapours by a photopyroelectric (PPE) sensor. The PPE sensor consists of a pyroelectric detector covered with a sensitive polymer film. The vapour is sorbed within the film and excited by infrared radiation. The heat obtained by thermal relaxation depends on the amount of sorbed vapour. Finally, the electrical output of the pyroelectric detector is a function of the vapour concentration. The use of monochromatic light guarantees high selectivity. This is shown for a PPE sensor, covered with polyvinylpyrrolidone, detecting a mixture of water and methanol vapour. Furthermore, PPE spectroscopy is used to find suitable infrared wavelengths for improving the detector sensitivity. The PPE signal as a function of methanol vapour concentration and methanol mass loading within the sensitive polyvinylpyrrolidone film shows that the best sensitivities are given at low concentrations. The partition coefficient characterizing the quantity of sorption of the polymer film indicates that a polyvinylpyrrolidone-covered sensor exhibits a higher sensitivity for methanol than for dichloromethane.