Recent near infrared observations of starburst galaxies and
 active galactic nuclei have revealed that such objects are
 often prominent sources of forbidden [Fe II] emission lines at
 1.26 and 1.64 microns.  The origin of the [Fe II] emission is
 uncertain and has been attributed to hot gas in HII regions,
 photon-dominated regions, or supernova remnants associated
 with star-formation, and to X-ray irradiated or shocked gas
 associated with non-stellar energy sources in active galactic
 nuclei. Identification of the primary [Fe II] emission sources
 is crucial in order to use the Fe II emission lines as
 quantitative diagnostics of processes in SBGs and AGNs.

 The ISO SWS offers the opportunity to study such infrared [Fe II]
 emission sources in a way never attempted before.  We propose
 to use the SWS to observe the mid-infrared 5.34, 17.93, and
 25.98 micron lines of [Fe II] in a sample of objects containing
 Seyfert 1's and 2's, and starburst galaxies. Our measurements
 will provide new constraints on the physical conditions in the
 [Fe II] emitting regions, and will provide unique information
 about the gas temperatures, densities, sizes and iron abundances
 in them. Our model computations show that these lines should be
 easily detectable in galaxies which produce bright near infrared
 [Fe II] emission.

 Our proposed observations will complement several SWS measurements
 of Galactic [Fe II] emission sources which will be carried out
 within the Central Programme. Our ISO observations will provide
 crucial new information about the nature of infrared extra-
 galactic [Fe II] emitters.