Metacomputing is an emergent paradigm that makes possible to distribute applications over a heterogeneous set of computing systems to exploit all available resources. The paper presents the HPO environment for object-oriented metacomputing. The HPO programming model is based on the object-oriented paradigm and defines architecture-independent and portable applications. The HPO support makes it possible to distribute applications over a network of heterogeneous architectures. The paper describes this approach via several examples and evaluates its achieved performances.