This chapter discusses the establishment of a transfected mouse fibroblast cell line, which expresses a novel rat dopamine D2 receptor subtype. In this chapter an approach is used, which involves the cloning and characterization of genes for which no specific antibodies or sequence information exists. The central strategy involves transfer of genomic DNA or cDNA sequences into a heterologous cell type, which does not express the gene of interest. The transfected cells are then screened for de novo expression of the gene of interest and single clones of cell lines isolated. The cell line can then be used for characterization of the expressed sequences with respect to either physiological or pharmacological properties. The cell lines can also be used as a starting source of material to subsequently clone and characterize the transfecting element. This type of strategy is particularly attractive for the cloning of cell surface proteins, which are in low abundance and are difficult to purify.