Continuous monitoring of a computer network performance is probably the only solution which allows prompt identification of anomalous functioning conditions and knowledge of parameters on which to base speedy, effective recovery interventions. A number of tools for performance management already exist, but their effectiveness is limited as they are essentially inserted inside owner network management solutions. In the paper we describe the realization of PMt, a platform for the development of performance management applications for the control and real-time management of a heterogeneous computer network. PMt imposes an object-oriented view of the distributed system, defines a performance management design methodology which adapts well to really distributed system management and provides the user with a set of tools and services to assist him both in the design of new performance management applications and in actual management of the whole system.>