The main aim is to study the effects of the presence of a
 nearby companion, and of a central bar (i.e. the effects of
 gravitational perturbations) on the gas properties and
 star-formation activity in spiral galaxies. This kind of
 statistical study has been carried out in the radio-continuum
 emission, in Halpha and in CO emission: the inter-comparison
 of these results with FIR lines will allow a deeper understanding
 of large-scale physical processes leading to star formation.