High resolution Fourier transform mid-infrared absorption spectroscopy is a powerful method for the analysis of trace constituents in the atmosphere. Most lightweight molecules can be detected at concentrations down to approximately 100 ppb in five liter samples. Once programmed, the computer aided analysis of qualitatively similar samples proceeds rapidly, the throughput rate reaching one sample every ten minutes, including printout. For ambient atmosphere analysis, extremely long absorption path lengths result in detectivities down to a few parts per billion.