Rhea is an expert-curated knowledgebase of chemical and transport reactions of biological interest. Enzyme-catalyzed and spontaneously occurring reactions are curated from peer-reviewed literature and represented in a computationally tractable manner by using the chemical dictionary ChEBI (Chemical Entities of Biological Interest) to describe reaction participants.

Rhea reactions are described independent of their biological location (subcellular location, tissue, organ, species) and are chemically balanced at pH 7.3. Rhea covers the reactions described by the IUBMB Enzyme Nomenclature as well as many additional reactions and can be used for enzyme annotation, genome-scale metabolic modeling and omics-related analyses. Rhea has become the standard for enzyme and transporter annotation in UniProtKB.

Rhea is freely available and accessible in different formats.