Reactome is a free, open-source, open-data, curated and peer-reviewed 
knowledgebase of biomolecular pathways. One of its main priorities is to provide 
easy and efficient access to its high quality curated data. At present, 
biological pathway databases typically store their contents in relational 
databases. This limits access efficiency because there are performance issues 
associated with queries traversing highly interconnected data. The same data in 
a graph database can be queried more efficiently. Here we present the rationale 
behind the adoption of a graph database (Neo4j) as well as the new 
ContentService (REST API) that provides access to these data. The Neo4j graph 
database and its query language, Cypher, provide efficient access to the complex 
Reactome data model, facilitating easy traversal and knowledge discovery. The 
adoption of this technology greatly improved query efficiency, reducing the 
average query time by 93%. The web service built on top of the graph database 
provides programmatic access to Reactome data by object oriented queries, but 
also supports more complex queries that take advantage of the new underlying 
graph-based data storage. By adopting graph database technology we are providing 
a high performance pathway data resource to the community. The Reactome graph 
database use case shows the power of NoSQL database engines for complex 
biological data types.