Administrative functions are often performed by judges. The separation of powers is an ordering principle of the Italian constitutional system. However, it is not observed in absolute terms in positive law. This overlap between functions and powers can be considered physiological, with respect to a complex legal reality. Conversely, the observation highlights different situations in which the ‘overflow’ of jurisdictional power into administrative power becomes problematic. Through the study of three concrete cases, this article aims to identify the reasons for and the tendential implications of this overflow. The weakness of the administration creates gaps that tend to be filled by the judiciary. This does not lead to a rebalancing. The administration’s decisions are taken, according to the rules of the administrative procedure, based on administrative discretion. Such discretion naturally cannot pertain to judges. To revive of the separation of powers, in terms of ‘administration reserve’, it is essential that the administration itself becomes more solid. The achievement of this objective passes through defence of the merit-based selection of the staff of the public administration, which endows them with the neutrality required under the Constitution.