Observations and diagnostic use of highly redshifted fine structure lines

The diagnostic use and detectability of luminous fine structure lines from high redshift galaxies is reviewed in the light of results from COBE concerning the Milky Way and from ISO on low redshift galaxies. At the highest luminosities (L>10^{12}\Lsun) the [CII] 158 micron line is somewhat less luminous with respect to the bolometric luminosity than for lower luminosity objects. Thus, surveys for this line must emphasize depth. The [CII] line will be the principle spectroscopic probe of the deep universe for the MMA and FIRST. A deep search for [CII] 158 micron emission from the dusty z=4.693 quasar BR1202-0725 is presented. The resulting 3\sigma upper limit implies that for this object L[CII]}/LFIR<0.0006%, a highly significant result indicating that distant luminous objects may represent a natural extension towards higher luminosities of the ultraluminous infrared galaxies at low redshift.