Growing legal requirements in terms of the identity and quality control of chem. products increasingly require the use of anal. techniques which can be applied solvent- and destruction-free or which can be directly implemented in a process to provide real-time information. With the vibrational spectroscopic techniques of mid-IR (MIR), near IR (NIR) and Raman spectroscopy in combination with special probes and chemometric evaluation procedures, such tools have become available and are gaining increasing importance for industrial process monitoring. The present communication reports the results obtained by online light-fiber coupled Fourier transform near IR (FT-NIR) transmission spectroscopy and Fourier transform mid IR (FT-MIR) spectroscopy in the attenuated total reflection (ATR) mode to monitor the soln. polymn. of Me methacrylate.