  The role of planetary nebulae as probes for the galactic chemical evolution
is reviewed. Their abundances throughout the Galaxy are discussed for key
elements, in particular oxygen and other alpha elements. The abundance
distribution derived from planetary nebulae leads to the establishment of
radial abundance gradients in the galactic disk that are important constraints
to model the chemical evolution of the Galaxy. The radial gradient, well
determined for the solar neighborhood, is examined for distinct regions. For
the galactic anticenter in particular, the observational data confirm results
from galactic evolution models that point to a decreasing in the gradient slope
at large galactocentric distances. The possible time evolution of the radial
gradient is also examined comparing samples of planetary nebulae of different
ages, and the results indicate that a flattening in the gradient occurred,
which is confirmed by some galactic evolution models. The galactic bulge is
another important region whose modeling can be constrained by observational
results obtained from planetary nebulae. Results derived in the last few years
indicate that bulge nebulae have an abundance distribution similar to that of
disk objects, however with a larger dispersion.
