  A review of the main characteristics of low-latitude sources in the third
EGRET catalog is presented. There are 75 unidentified gamma-ray sources
detected by EGRET at less than 10 degrees from the galactic plane. About a half
of these sources are spatially correlated with potential galactic gamma-ray
emitters such as supernova remnants, OB associations and early-type stars with
very strong stellar winds. The other half is formed by sources without
positional correlation with known galactic objects capable to generate a gamma
ray flux significant enough as to be detected by EGRET. A variability analysis
shows that this second group of sources contains several objects with high
levels of gamma-ray variability. These variable sources resemble very much the
AGNs detected by EGRET, but without their typical strong radio emission. To
establish the nature of these sources is one of the most urgent problems of
high-energy astrophysics.
