We describe the ProGenGrid (Proteomics and Genomics Grid) Workflow system, developed by the CACT/ISUFI at the University of Lecce which aims at providing a tool that e-scientists can utilize to simulate biological experiments, compose existing analysis and visualization tools, monitor their execution, store the intermediate and final output and finally, if needed, save the model of the experiment for updating or reproducing it. The tools that we are considering are software components wrapped as Web Services and composed through a workflow. Since bioinformatics applications need to use high performance machines or many workstations to reduce the computational time, we are exploiting a Grid infrastructure for interconnecting wide-spread tools and hardware resources.