The goldfish odorant receptor 5.24 is a member of family C of G protein-coupled receptors and is closely related to the human receptor GPRC6A. Receptor 5.24 has previously been shown to have binding affinity for L-alpha-amino acids, especially the basic amino acids arginine and lysine. Here we report the agonist activities of the 20 proteinogenic L-alpha-amino acids, and L-ornithine and L-citrulline, measured in an intracellular calcium release assay in mammalian tsA cells. The results show that receptor 5.24 is broadly activated by 19 of the tested L-alpha-amino acids and displays a preference for basic amino acids.