ABSTRACT This contribution reports on the use of a FT-IR-spectrometer for measuring concentrations during the drying of thin films of Polyvinyl acetate (PVAc) and Methanol. Calibration was carried out by differential weighing. The spectra were taken in transmission mode while dried air was blown over the liquid films. The obtained accuracy was +/− (5% + 0,8 g/m2) for small contents of Methanol and +/− (10 % 2 g/m2) for higher Methanol contents. The content of PVAc could be measured with 5% accuracy. The experiments were carried out at room temperature; the examined films had a thickness of about 30 to 60 microns when completely dry.