In this paper we present first experiences concerning the integration of MPI-based numerical software into an advanced programming environment for building parallel and distributed high-performance applications, which is under development in the context of Italian national research projects. Such a programming environment, named ASSIST, is based on a combination of the concepts of structured parallel programming and component-based programming. Some activities within the projects are devoted to the definition, implementation and testing of a methodology for the integration of a parallel numerical library into ASSIST. The goal is providing a set of efficient, accurate and reliable tools that can be easily used as building blocks for high-performance scientific applications. We focus on the integration of existing and widely used MPI-based numerical library modules. To this aim, we propose a general approach to embed MPI computations into the ASSIST basic programming unit. This approach has been tested using the MPICH implementation of MPI for networks of workstations. Some modifications have been applied to the MPICH process startup procedure, in order to make it compliant with the ASSIST environment. Results of experiments concerning the integration of routines from a well-known FFT package are discussed.