Abstract: This invention relates generally to recombinant DNA techniques and to the expression of mammalian polypeptides in genetically engineered eukaryotic cells. Specifically, the invention relates to preferred plasmid constructs and methods that increase levels of expression of a cloned gene product. These preferred plasmids have selectable and nonselected gene cassettes adjacent to each other and oriented in the opposite direction for transcription. Such an orientation enhances overall levels of expression for the nonselected gene. Further, this invention relates to gene products expressed at these very high levels by the herein described method, and to the eukaryotic cells derived thereby.