CytoSaddleSum is a Cytoscape functional enrichment plugin that provides interface to SaddleSum functionality. It works by querying SaddleSum either locally (using the standalone version) or remotely, through an HTTP request to a web server. The results of a functional enrichment query are shown as a term relationship network, where nodes represent terms linked by edges showing term relationships. The statistics and other query details for each term are written as node attributes, allowing easy integration into network-based data analysis workflows.