  We report on a attempt to detect beryllium in two dwarf stars of the Galactic
halo with metallicities below one thousandth solar. The data were obtained
during the Commissioning of the Ultraviolet and Visible Echelle Spectrograph
(UVES) mounted on the ESO VLT Kueyen telescope, and show the potential of UVES
for studies in the UV-optical domain. We claim a beryllium detection in LP
815--43 ([Fe/H]~-2.95,[Be/H]=-13.09) at the 99.7% confidence level, while only
an upper limit can be set for the second target CD -24 17504 ([Fe/H]~-3.30,
[Be/H]~-13.39). These results suggest that the trend of beryllium with
metallicity keeps decreasing as lower metallicities are probed, with no
evidence for flattening. In CD -24 17504 we also analyzed the Li I line at
6708A, and derived a lithium abundance close to the Spite plateau.
