  Variability is a main property of active galactic nuclei (AGN) and it was
adopted as a selection criterion using multi epoch surveys conducted for the
detection of supernovae (SNe). We have used two SN datasets. First we selected
the AXAF field of the STRESS project, centered in the Chandra Deep Field South
where, besides the deep X-ray surveys also various optical catalogs exist. Our
method yielded 132 variable AGN candidates. We then extended our method
including the dataset of the ESSENCE project that has been active for 6 years,
producing high quality light curves in the R and I bands. We obtained a sample
of ~4800 variable sources, down to R=22, in the whole 12 deg^2 ESSENCE field.
Among them, a subsample of ~500 high priority AGN candidates was created using
as secondary criterion the shape of the structure function. In a pilot
spectroscopic run we have confirmed the AGN nature for nearly all of our
candidates.
