A volcano-tectonic crisis with strong seismic activity and rapid uplift started in 1982, and continued until its abrupt disappearance at the beginning of 1985, at Campi Flegrei caldera (Southern Italy). The chemical composition of the fumarolic fluids has been recorded during the last five years and, from geochemical and thermodynamical considerations, it has been deduced that the shallow reservoir feeding the fumaroles remained chemically isolated, at least with respect to major magmatic components, from the magma chamber inferred to be located at depth. ¿ American Geophysical Union 1988