  The origin of the abundance discrepancy in nebulae is one of the key problems
in the physics of photoionized nebulae. In this work we have analized a sample
of Galactic and extragalactic H II regions where the abundance discrepancy have
been measured, and we discuss the two main scenarios proposed to explain such
discrepancy: temperature fluctuations over the observed volume of the nebulae
and chemically inhomogeneous inclusions.
