The latest stage of the development of the Western Carpathian Arc and the Pannonian Basin was characterized by a lithospheric disintegration which occurred as a consequence of the transition from a transpressional to an extensional regime. This process was accompanied by both crustal thinning and, what is more important by thinning of the lithosphere. The thinning of the lithosphere was associated with an uplift of asthenospheric, partially molten masses, accompanied by local asthenoliths. This paper discusses the geological features and the development of processes involved in the ascension of partially molted masses into subcrustal levels through the older discontinuities. Geophysical and petrological evidence have shown that the uplift of these local partially molten masses nearly reached the Moho discontinuity. The mantle xenoliths transported to the surface by the youngest alkaline basalts and the study of their phase transition give petrological evidences for this process. Further geophysical indications of this process are seismic and magnetotelluric sounding (MTS) anomalies and geothermal conditions. The interpretation of other seismic profiles with prolonged registration, density and partly geomagnetic modelling have also been used in the interpretation. These data are discussed in the light of present knowledge of the tectonic development of Western Carpathians and the Pannonian Basin.