We propose to search for widely-separated cool brown dwarf
 companions to young nearby stars, using ISOCAM. Ground-based
 direct observations are not sensitive to cool brown dwarfs
 and ground-based indirect observations are incapable of
 detecting widely-separated brown dwarf companions. The mid
 infrared imaging capability of ISO provides us with a unique
 opportunity to search for  widely-separated cool brown dwarf
 companions (separation > 3 arcsec, T < 500 K).
 The high sensitivity of ISO to the cool brown dwarfs implies
 that the search limit can be extended to very low-mass
 brown dwarfs by selecting young nearby stars as targets.
 The ISOCAM survey will be sensitive to 0.01 and 0.03 solar mass
 brown dwarfs at 10 pc of the Sun respectively for ages,
 one and five billion years.
 It is well known that the chromospheric activity indicated
 by H alpha emission is associated with young stars.
 We have completed a CCD spectroscopic survey of 2000 nearby M
 dwarfs at Palomar and the complete set of emission line M
 dwarfs is available for us.
 We have selected 42 M dwarfs based on four criteria:
 1) H alpha  emission,     2) tangential velocity < 40 km/s,
 3) distance < 15 pc,      4) |b| > 40 deg.
 We estimate that the average age of our sample is order of
 one billion years, while that of the entire nearby stars
 is more than five billion years. We have an on-going program
 to search for brown dwarfs around nearby stars by coronagraphy.
 We will obtain coronagraphic images of all the fields to identify
 any field objects. Our observing method is identical to that
 of the Guaranteed Time Program by Telesco, but the target
 selection strategy distinguishes our proposal.