The size-frequency distribution of asteroids with diameters < 10 km
 is essentially unknown. We propose to use ISOCAM (LW3, CAM01) in
 microscanning mode to test current predictions of the number of
 asteroids per square degree down to sizes below 1 km. Our objective
 is to measure the number of asteroids per unit area of sky observed
 as a function of IR brightness. (A 1 km main-belt asteroid has a
 flux density at 15 microns of about 1 mJy.) From these data we will
 be able to constrain, and perhaps decide among, current estimates
 for the numbers of asteroids with diameters greater than 1 km.
 These estimates differ by up to a factor of six. Any region of sky
 along the ecliptic is suitable for this purpose and so the target
 regions are independent of the launch date. In addition to the solar
 system science resulting from this study, we will provide data
 useful for assessing the "contamination" rate from asteroids in all
 ISOCAM observations.