A laser heterodyne spectrometer with a tunable diode laser as a local oscillator has been developed for ultrahigh resolution IR spectroscopy of the absorption spectra of trace constituents in the earth's atmosphere. The spectral resolution and SNR of the developed system are 0.0013 cm(-1) and ~500, respectively. This performance is sufficient for retrieving the altitude profile of atmospheric O(3) through an inversion method. The altitude profile of atmospheric N(2)O has been also obtained for the first time with this laser heterodyne technique. The high resolution and high SNR have been accomplished by adopting a tunable diode laser which operates at liquid nitrogen temperature and by developing an effective technique to eliminate the optical feedback of the local oscillator laser beam.