A new type of high pressure spectroscopy view-cell for investigation of multiphase reactions is presented. It allows visual observation of the reaction mixture at conditions up to 200 °C and 200 bar. Measurements of the reactor cell’s upper part by transmission spectroscopy with variable path length and of the cell’s bottom part by attenuated total reflection (ATR) spectroscopy can be performed quasi-simultaneously. By coating the internal reflection element with a catalyst film, in situ investigations of heterogeneous catalysts can be performed. The potential of this new experimental setup is demonstrated using examples of heterogeneous and homogeneous catalytic reactions. For the heterogeneously catalyzed hydrogenation of ethyl pyruvate over Pt/Al₂O₃ in “supercriticalâ€� ethane the reaction progress could be monitored by spectroscopic investigation of the fluid phase. Quantitative evaluation of the spectra combined with digital imaging of the reaction mixture allowed simultaneous determination of phase behavior and reaction kinetics. ATR-IR spectra of the catalyst film could be measured at the same time. In the homogeneously catalyzed formylation of morpholine with “supercriticalâ€� carbon dioxide and hydrogen, not only number and nature, but also the composition of the different phases could be determined. The catalyst was found to be confined to the liquid phase. Although the aim of these preliminary studies was to test the functionality of the new cell, already significant new insight on the investigated catalytic reactions could be gained.