Abstract. We describe a programming interface for parallel computing on NUMA (NonUniform Memory Access) shared memory machines. Although the interest in this architecture is rapidly growing and more and more hardware manufacturers offer products of this type, there is still a lack in parallelization support. We developed SMI, the Shared Memory Interface, and implemented it as a library on an SCI-coupled cluster of workstations. It aims at providing sophisticated support to account for the NUMA performance characteristic and to allow a step-by-step parallelization. We show it’s application to the parallelization of a sparse matrix computation.