Within the field of second language acquisition the question of cessation of learning short of the target language norms, particularly among adult populations, has been widely discussed since the term FOSSILIZATION was first coined by Selinker in 1972. This article briefly outlines the main theoretical concerns of this phenomenon, which has had various terminological badges over the past three decades. It then details an experimental study whose aim it was to uncover the destabilising potential of instruction on the pronunciation of advanced French learners of English as a Foreign Language who displayed fossilization tendencies. The results indicate significant improvements made by the experimental group relative to the control group. In conclusion it is deemed appropriate to classify such learners as stabilised and not permanently fossilized as changes in pronunciation systems can occur given optimal conditions of learning and exposure.