Nowadays, Information Agents are widely exploited for implementing several typologies of Web services, on one hand, and for assisting users in interacting with Web services, on the other hand. However, agents often use different, heterogeneous ontologies, i.e. conceptual dictionaries, for representing the realities of their associated users and services; therefore a key issue in this context is ... [Show full abstract] that of making reciprocally understandable the meaning of terms contained in the exchanged messages. Such an issue can be faced by using a sem antic negotiation framework, in which agents try to understand each other by negotiating the semantic of the terms. Though several models of semantic negotiation have been proposed in the past, most of them are not able to support negotiation without requiring agents either to share knowledge or to use a global common ontology, and none of them provides a semantic negotiation protocol that allows the whole agent community to contribute to the semantic understanding process between each agent pair. In this work, we propose to use a new protocol, called HIerarchical SEmantic NEgotiation (HISENE), for supporting agents in the context of Web services, that gives a solution to the aforementioned problems. We also give an implementation of the proposed protocol as an extension of the standard JADE middleware.