[en] The search for extraterrestrial and, in particular, interstellar molecules has suddenly increased in the last ten years after the discovery of many complex organic molecules by radioastronomy. Since some very interesting lines are not detectable in the radio region, but only in the middle and far infrared, heterodyne techniques seem to be a powerful tool for interstellar line detection in the submillimetric region and the detection of CO at 870 μ in Orion (Philipps and Huggins, 1977) represents an encouraging success for further efforts in this new field of research. In this work of possibility of observing interstellar lines at heterodyne laser wavelengths already available in laboratory has been considered. Relative intensities for some representative rotational lines of interstellar molecules at three typical temperatures (10, 20, 50 K) have also been computed assuming thermodynamic equilibrium and optically thin regions. The results achieved with hetrodyne laser techniques developed in the laboratory are discussed here in order to study the possibility for ground and space astronomical observations. (Auth.)