Medusa is an interaction graph viewer and editor. A Graph is composed of nodes and edges, where edges indicate an interaction between two nodes.Medusa is a front end (interface) to the STRING protein interaction database. It is also a general graph visualization tool. The STRING web interface, while extensive, is static. It does not allow users to create their own networks, enhanced with STRING interactions. Medusa gives you much greater freedom in manipulating STRING data. As a general tool, Medusa is very easy to use and flexible. Users can load their own data or interactively add or delete nodes and edges. It is also free for academic use and easy to install. Medusa was originally a house tool at EMBL and has been used in a number of successful scientific projects. We hope that others too can benefit from Medusa.Requires Java Runtime Environment. Get It Here.