We propose to obtain accurate photometry at 60 micron for a subsample of 100 out of the 1500 G dwarfs that will be monitored for the presence of substellar companions with the high-precision radial-velocity spectrometer CORALIE at the new Swiss telescope that will be installed in 1997 at La Silla Observatory, Chile. The ground-based observations will enable a statistically significant discussion of the occurrence of Jupiters and brown dwarfs and of their orbital parameters. The ISOPHOT data will enable that of the occurrence of dust debris disks which are thought to be related to the planetary systems; no instrument other than ISO can do this during the next decade, i.e. the epoch during which important progress in our knowledge of the presence of giant planets around stars is expected. The combination of radial-velocity surveys and ISO observations will reveal the relation between the occurrence of both phenomena and therefore is a unique test of planet-formation scenarios.