The asteroid belt contains a record of the thermal
 evolution of the early solar-system, with the more
 distant asteroids containing volatile compounds that
 escaped heating by the sun. The reddish, low-albedo
 D-type asteroids that dominate the outer asteroid belt
 possess optical properties characteristic of organic
 compounds. Unfortunately their exact surface composition
 remains unknown, as diagnostic bands of organic molecules
 lie at short infrared wavelengths (2-12 microns), and few
 are accessible from ground-based observatories.

 We propose to investigate this wavelength region in 4-5
 D-type asteroids with ISO. Our primary aim is to identify
 the exact surface composition of these bodies. By comparing
 individual asteroids, degrees of variation in composition will
 be searched for. Findings from this investigation will provide
 the first observations by which previous laboratory studies
 may be compared.