  Current detection methods of planetary companions do not allow retrieving
their spectral information properties. The method of Differential
Interferometry has the potential to complement such information by comparing
interferometric observables in various spectral channels. We outline the basic
aspects of this method and how it can soon be realised by the Mid-infrared
Interferometric instrument (MIDI) at the Very Large Telescope Interferometer
(VLTI) observatory. A set of possible candidates for such direct observation
has been selected among currently identified planetary companions. Differential
Interferometry with MIDI would be complementary to other ground-based programs.
The method may also be an alternative for future space-based planetary
spectroscopy.
