We propose to make ISOCAM and ISOPHOT observations of candidate high-redhift luminous infrared galaxies selected from the IRAS Faint Source Database. The prototype, IRAS F10214+4724 at z=2.286, implying L_ir 10^14 L_sun and M_H2 10^11M_sun, is the most infrared-luminous and gas-rich object known. It may be the first discovered, long sought, protogalaxy, although it also has some quasar-like properties. We have selected faint (S_60 < 0.3Jy), high S_ir/S_optical (nu*S_60/nu*S_blue > 30) extragalactic sources in the FSDB using the IRAS OptID database. The majority of these are blank optical fields (b > 21) from digitized (COSMOS) survey plate data of the southern sky. The well-established correlation between IR/Optical ratio and FIR luminosity translates the above selection into high luminosity (L_ir > 10^12L_sun), which, combined with the S_60 limit, selects for high-redshift (z > 0.3). Our sample is the result of the best possible systematic search through the entire all-sky IRAS database for the deepest (infrared) and faintest (optical) fields (using the high quality SERC/UKSTU survey plates), and thus represents the best all-sky sample for cosmology. ISOCAM images at 12um will determine accurate positions for these sources and allow positive optical identification. Combined with ISOPHOT measures at 90um and 180um and existing IRAS 60um flux-densities, these will determine the infrared spectral-energy distributions, infrared luminosities and dust masses for a sample of 98 of the best candidates.