  We present results of deep echelle spectrophotometry of eight Galactic HII
regions located at Galactocentric distances between 6.3 and 10.4 kpc. The data
have been taken with the Very Large Telescope (VLT) Ultraviolet Echelle
Spectrograph (UVES) in the 3100 to 10360 A range. We have derived C++ and O++
abundances from recombination lines for all the objects, as well as O+
abundances from this kind of lines for three of the nebulae. The intensity of
recombination lines is almost independent of the assumed electron temperature
as well as of the possible presence of spatial temperature variations or
fluctuations inside the nebulae. These data allow the determination of the
gas-phase C and O abundance gradients of the Galactic disk, of paramount
importance for chemical evolution models. This is the first time the C gradient
is derived from such a large number of HII regions and for such a wide range of
Galactocentric distances. Abundance gradients are found of the form
$\Delta$log(O/H) = -0.044$\pm$0.010 dex kpc^-1, $\Delta$log(C/H) =
-0.103$\pm$0.018 dex kpc^-1, and $\Delta$log(C/O) = -0.058$\pm$0.018 dex
kpc^-1.
