In this paper we present DockFlow, a prototypic version of a PharmaGrid. DockFlow is supporting pharmaceutical research through enabling virtual screening on the Grid. The system was developed in the course of the BRIDGE project funded by the European Commission. Grids have been used before to run compute- and data-intensive virtual screening experiments, like in the WISDOM project. With DockFlow, however, we addressed a variety of problems yet unsolved, like the diversity of results produced by different docking tools. We also addressed the problem of analysing the data produced in a distributed virtual screening system applying a combinatorial docking approach. In DockFlow we worked on a grid-based problem solving environment for virtual screening with the following major features: execution of four different docking services (FlexX, AutoDock, DOCK and GAsDock) at locations in Europe and China remotely from a common workflow, storage of the results in a common Docking Database providing a shared analysis platform for the collaboration partners and combination of the results. The DockFlow prototype is evaluated on two scientific case studies: malaria and avian flu.