An interdigitated array electrode (IDA) is fabricated on an IR-transparent substrate for use in electrooptical measurements using Fourier transform infrared (FT-IR) spectroscopy. The fabrication of the IDA and its unique sampling geometry for transmission spectroscopy is detailed. The gold IDA was patterned on the ZnSe substrate using a photolithographically defined liftoff process. An IR flow cell was modified to enable the substrate containing the IDA to be used for electrooptical measurements in transmission. The utility of the electrooptical cell is demonstrated by application to two model systems. In the first, changes in the conductivity and spectral features of a receptor membrane (Nafion) upon dehydration are measured. In the second, the measurement of the electric-field-induced orientation of a liquid-crystalline film of 4-n-pentyl-4'-cyanobiphenyl was conducted in a new experimental geometry, with IR transmission normal to the direction of the applied electric field. Difference spectroscopy facilitated the observation of the change in orientation of the liquid crystal with applied potential. These systems demonstrate the general utility of the fabrication scheme described here. It also illustrates its facile adaptation to infrared difference spectroscopy as a means of studying complex phenomena in electrochemical and electrooptical systems.