Institut d'Astrophysique Spatiale, Orsay, France
ISO has has provided a wealth of new spectroscopic
information in the wavelength range
2.4 to 196 
towards various interstellar regions.
In particular, the spectrometers on board of ISO have
allowed to make significant progress in our understanding
of the densest parts of the interstellar medium.
Results of combined SWS-LWS grating spectra which have been obtained towards a number of galactic compact HII regions will first be presented. These data allow a complete inventory of the main atomic and molecular emission lines in these sources and their variations along the galactic disk.
The second part will focus on observations obtained at higher spectral resolution with the LWS Fabry-Pérot on SgrB 2 and Orion BN/KL. These observations reveal a wealth of emission and absorption lines which will be presented and discussed with an emphasis on the detection of species other than water vapour.