  Recently much work has been done in lowering the Planck threshold of quantum
gravitational effects (sub-millimeter dimension(s), Horava-Witten fifth
dimension, strings or branes low energy effects, etc.). Working in the
framework of 4-dim gravity, with semi-classical considerations based on Hawking
evaporation of planckian micro-black holes, I shall show here as quantum
gravity effects could occur also near GUT energies.
