==>In this proposal, more time is being requested for CFANTI.CSS_GPS ==>This proposal requests an upgrade from Priority 3 for CFANTI.CSS_GPS (part) ============================================================================== This proposal is an extension and completion of a previously approved one, to search for infrared emission from Compact Steep Spectrum (CSS) and GHz Peaked Spectrum (GPS) radio sources. CSS and GPS are powerful extragalactic radio sources with radio emission confined well within their host galaxies. They are thought to be either young objects, which have yet to develop extended radio lobes, or sources where the radio emitting plasma is trapped by an unusually dense interstellar medium. By searching for emission from cold dust, we will determine which of the two scenarios is correct. In the former case, CSS/GPS will have as much cold gas and dust as comparable power large size FRII sources. In the latter case, they should be the most logical group of high red-shift object in which to search for gas and dust, allowing us to extend the work on gas rich galaxies to much higher red-shifts than IRAS was generally able to reach. Therefore this sample represents an excellent chance of finding distant analogues to the ultraluminous IRAS galaxies. IRAS observations of CSS/GPS were inconclusive, due to the limited sensitivity and the comparatively "short" observing wavelengths of that mission coupled with the spread of redshifts in these sources (generally considerably more distant than IRAS detected galaxies). With ISOPHOT, even taking into account the reduced level of the performances of the instrument, we may detect fluxes at a level a FACTOR 5 LOWER THAN IRAS. In the previous proposal we asked to observe a sample of CSS/GPS radio galaxies together with a comparison sample of extended objects, to determine whether there is indeed an unusually dense and cold ISM in the host galaxies of CSS/GPS radio sources as compared with extended radio galaxies. Here we repropose the observation of the objects of the previous proposal, mostly from the reference sample, which were given priority 3 (unlikely to be observed) plus a few others which have been found in these years to have properties that make them part of the original sample.