In this paper we present GAIN (Grid Agent INfrastructure), a multi-agent system that can be used for the development and deployment of flexible agentbased Grid systems. Through the use of the agents jointly with the workflow and Web service technologies, we are able to support the users in the development and execution of Grid applications. In particular, the GAIN system allows the definition of workflow applications by composing heterogeneous tasks and follows the different phases of the workflow execution, providing transparent allocation of the tasks on the different nodes of the Grid. A first prototype of the system has been completed using the JADE agent development software and also some lab trials have been executed involving a small network of different JADE platforms.