PathHunter eXpress β-Arrestin kits are complete, assay-ready kits that provide a robust and easy-to-use, cell-based functional assay to study GPCR activity through β-arrestin recruitment. The pre-validated, frozen eXpress cells have been manufactured for single-use and are provided in a convenient, ready-to-screen format that eliminates the need for lengthy, expensive and time-consuming cell culture, making functional testing fast and convenient.