The article examines the most relevant legal aspects of the liberalization of national public monopolies. The focus is on the evolution of the jurisprudence of the Court of Justice at a time when some features of the process of liberalization at E.C. level is not completely clear. The article offers a possible way to interpret the jurisprudence of the Court on public monopolies outlining a criterion of evaluation of the legitimacy of State measures that grant exclusive rights based on the different levels of inducement to abuse of the undertakings benefiting from the exclusive rights. The article then examines the possible objective justifications of the national monopolies of services of general economic interest through an analysis of the derogation set in article 90.2 of the Treaty as interpreted in the sentences of the Court, while carefully maintaining the balance of the system.