This work describes the implementation and benchmarks applied to a load balancing software designed to improve perfonnance of parallel applications running on networks of heterogeneous and non-dedicated workstations. A user leveI mechanism to gather workload infonnation about each node and the policy to treat this infonnation in order to generate a precise snapshot of the workload of each node of the parallel machine are described throughout this work. An analysis of the main issues concerning workload evaluation is provided, along with a brief explanation on the support o.ffered by current operating systems and ways to overcome their problems. Finally, results and interpretations of comparative tests made between BEC/PVM applications and PVM applications are presented.