Abstract: The invention provides insect cell-based systems for assaying G-protein-coupled receptor interactions. The insect cells may express a heterologous mammalian G-protein-coupled receptor, a heterologous G alpha protein and one or more insect effector proteins that couple the heterologous G alpha protein to an endogenous insect signalling pathway. In such systems, binding of a ligand to the heterologous G-protein coupled receptor mediates a detectable change in the insect cell. The protein components of the system may be expressed from coding sequences that are stably maintained by transformed insect cells.