Abstract : Expresso is a Java library dedicated to cluster-based computing on a high speed network. It aims at providing objects exchange capabilities to an object oriented language as MPI or PVM provides values exchange capabilities to procedural languages through the message passing paradigm. Expresso does not introduce a new object distributed model; the emphasis is on performance rather than on expressiveness: very fast object transfer between two machines is achieved thanks to a direct memory to memory dump in replacement of the usual marshalling of structured values. We develop the ISO-address concept to manage the memory on the network nodes and implement it upon available communication libraries. Experimental results demonstrate a dramatic change in the objects transfer speed. Application programmers or higher level libraries are able to capitalize on such communication mechanism and to exploit the potential of high speed network even through an object language.