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.