The OptiCHO Express Kit provides for the efficient growth and transfection of dihydrofolate reductase-deficient (DHFR-) Chinese hamster ovary (CHO) DG44 cells in suspension culture. The kit provides a complete workflow protocol for the development of stable cell lines and includes all of the necessary components for expression vector construction, transfection of DG44 cells, and recombinant protein expression in a serum-free environment with animal origin-free media.