Our main scientific goal is to identify cometary activity in a number
 of asteroids thought to be of cometary origin. Up to 50% of near-Earth
 asteroids are suspected of being evolved or dormant comets. However,
 conclusive evidence of this in the case of any particular asteroid
 remains elusive, despite the considerable efforts devoted to this
 question in recent years by groups working with ground-based
 instruments. The best technique to date uses high-resolution surface
 photometry to search for faint visible comae extending beyond the
 seeing disk. Unfortunately, the best sensitivity achievable
 corresponds to a mass-loss rate of ~0.1 kg/s, which is expected to be
 the upper limit for near-Earth cometary asteroids. We propose to
 search for thermal emission from dust comae around 9 such objects with
 ISOCAM using the 11.5 micron filter. The sensitivity of the ISOCAM
 observations should better the current state-of-the-art ground-based
 efforts by about an order of magnitude.

 A further objective is to gain information on physical characteristics
 of these targets, such as sizes and surface properties, by performing
 multi-filter photometry with ISOPHOT throughout the range of their
 thermal emission (5 - 60 microns). ISOPHOT offers a unique opportunity
 to carry out these measurements over the entire mid-infrared range and
 obtain an accurate thermal spectrum for each target at a well defined
 point in time. In cases where sizes and rotation parameters are known,
 this unique set of data will enable asteroid thermal models to be
 refined.