This project was performed by an international collaboration of French, German, Italian, Israeli, Polish and American scientists led by the Max-Planck-Institut für Kernphysik Heidelberg.
After brief interruption, the experiment was continued under a new name GNO (Gallium Neutrino Observatory) from May 1998 to April 2003.
It was designed to detect solar neutrinos and prove theories related to the Sun's energy creation mechanism.
The experiment's main components, the tank and the counters, were located in the underground astrophysical laboratory Laboratori Nazionali del Gran Sasso in the Italian Abruzzo province, near L'Aquila, and situated inside the 2912-metre-high Gran Sasso mountain.
Its place under a depth of rock equivalent of 3200 metres of water was important to shield from cosmic rays.
During the period 1991-1997, the detector measured capture rate of 73.1 SNU (Solar neutrino units).
After the end of GALLEX its successor project, the Gallium Neutrino Observatory or G.N.O., was started at LNGS in April 1998.