We propose to make medium-resolution (R = 1000) spectroscopic
 observations of Titan in the 5-to-7 mum range. This part of the
 spectrum contains important information in three fundamental
 areas of Titan's physico-chemistry: the organic haze, the
 surface, and the high-altitude photochemistry. Theoretical
 modeling of Titan's radiation show that this wavelength interval
 corresponds to the transition between reflected sunlight and
 thermal emission. The two components should be of equal intensity
 near 6.0 mum, and the spectral shape of that transition should
 be mostly diagnostic of the haze optical properties. The proposed
 measurements would provide a definite test of the tentative
 identification of the haze material with laboratory-synthesized
 organics or "tholins". At shorter wavelengths, current models as
 well as spectrally-resolved observations at 1-5 mum, suggest that
 the haze becomes more transparent, allowing to sense the surface
 or near-surface layers. Albedo measurements between 5 and 6 mum
 would provide crucial information on the composition and physical
 properties of the surface, and hence, on the origin and evolution
 of Titan. At wavelengths longer than 6 mum, the thermal emission
 regime allows to probe warm stratospheric layers where
 photochemically-produced as well as exogenic molecular species
 in the vapor phase produce strong emission lines. The detection
 of such molecular transitions, in particular those of H2O near
 6.3 mum, would further our understanding of Titan's unique
 chemistry. The ISO satellite offers the sole opportunity to
 explore that part of the spectrum, since telluric water vapor
 absorption makes such observations impossible or at best very
 uncertain from ground-based or airborne observatories. Moreover,
 the Cassini/Huygens instrument payload will not permit remote
 observations in that range.