  Hubble Space Telescope NICMOS observations are presented of six brown dwarf
candidates in the Pleiades open cluster. One of them, namely CFHT-Pl-18, is
clearly resolved as a binary with an angular separation of 0".33. The very low
density of contaminating background stars in our images and the photometry of
the components support that this system is a physical binary rather than a
chance projection. All the available photometric and spectroscopic data
indicate that the CFHT-Pl-18 system is likely a member of the Pleiades cluster,
but a final confirmation will have to wait until lithium can be detected.
Assuming cluster membership, we compare our NICMOS photometry with evolutionary
models, and find that the inclusion of the effects of dust grains is necessary
for fitting the data. We estimate that the masses of the components are about
0.045 Msol and 0.035 Msol. The binary system has a projected separation of 42
AU (for a distance of 125 pc) that is common among stellar binaries.
