  The Upper-Scorpius association is the OB association nearest to the Sun (145
pc). Its young age (5 Myr) makes it an ideal place to search for low-mass stars
and brown dwarfs, as these objects should be relatively bright. We have
performed a photometric search for the low-mass members of the association,
using the R, I, and Z filters. The completeness limit is I=18.5 and the
saturation limit is I=13. We obtain 138 candidate members, covering nearly the
entire M spectral type range. We find an excess of brown dwarf candidates over
the number predicted by a Miller-Scalo Initial Mass Function. In addition, we
have performed infrared imaging and low resolution optical spectroscopy of
selected candidates. We find that the infrared observations confirm the
spectral types obtained with the optical photometry. Furthermore, we find
H_alpha in emission in 20 of the 22 objects observed spectroscopically. As
H_alpha is an indicator of youth, we believe that these 20 objects may belong
to the association. One of them, UScoCTIO 128 has a very strong and constant
H_alpha line (equivalent width: -130 A), and its position in the color
magnitude diagram suggests that it is a brown dwarf with mass equal to 0.02
msun. Confirmation of this and the other candidates will have to wait for
higher resolution observations that can reveal spectroscopic mass indicators
like Li I and gravity indicators, such as K I and the subordinate lines of Na
I.
