  Using a long (=150 ksec), broad-band (0.1--40 keV) BeppoSAX observation of
the merging starburst system Arp 299 (=IC 694 + NGC 3690) we found the first
unambiguous evidence of the presence of a deeply buried (N_H = 2.5E24 cm-2) AGN
having an intrinsic luminosity of L(0.5-100 keV) = 1.9E43 cgs. The X-ray
spectral properties of this AGN are discussed in detail as well as the thermal
component detected at soft X-ray energies which, most likely, is associated
with the starburst.
