An experimental setup for Fourier transform infrared (FTIR) studies in condensed matter at high pressure and low temperatures is described. We have adapted a close-cycle cryostat(T=20–300K) to the sample compartment, which is used as a cryo chamber, of a FTIR spectrometer (frequency range 10–15 000cm−1).A Cassegrain-type beam condenser is assembled to measure infrared absorptions of samples contained in a membrane diamond anvil cell(Pup to 100 GPa). The tuning of the pressure and the cell alignment is performed from outside the evacuated instrument. An additional light path allows visual observation andin situpressure calibration. The advantages of this system, demonstrated by its application toCH4andAr–(H2)2crystals, are high radiation throughput, long time stability, visual observation of the sample, remote measurement and variation of the local pressure, and remote alignment of the cell with the IR beam. ©1997 American Institute of Physics.