Abstract: Methods for identifying a ligand of a G protein-coupled receptor (GPCR), such as ligands of orphan GPCRs, are provided. The methods include providing at least one cell containing a G-alpha protein that couples to at least one GPCR. The at least one cell is transformed with a recombinant DNA including a nucleic acid encoding a GPCR and the nucleic acid is expressed. At least one chemical compound is contacted with the transformed at least one cell and a calcium sensitive-fluorescent dye to form a first mixture. The at least one chemical compound is also contacted with at least one untransformed cell and the calcium sensitive-fluorescent dye to form a second mixture. Fluorescence from the first and second mixtures is measured and compared to determine whether the at least one chemical compound is a ligand of the GPCR. Nucleotide sequences, amino acid sequences, vectors, cells, and pharmaceuticals thereof are provided.