  We present results of an optical and near-infrared (IR) 1.8 deg^2 survey in
the Pleiades open cluster to search for substellar objects. From optical I-band
images from the CFHT and J-band images from the 3.5 m CAHA Telescope, we
identify 18 faint and very red L brown dwarf candidates, with I> 20.9 and I-J>
3.2. The follow-up observations of nine objects in the H- and Ks-bands confirm
that eight belong to the IR sequence of the cluster and the proper motion
measurements of seven candidates confirm that they are Pleiades members. A
preliminary estimation of the substellar mass spectrum dN/dM in the form of a
power law M^-alpha provides alpha=0.57+-0.14. We extrapolate this function to
estimate the number of very low-mass brown dwarfs and planetary mass objects
that could be present in the cluster down to 1 M_Jup. Sensitive searches
combining far red and near infrared observations may unveal these objects in a
near future.
