The market and fields of application for therapeutic proteins, such as monoclonal antibodies, are constantly growing. Therefore, stable production systems and high yields become increasingly important. CHO cells are widely used for expressing recombinant proteins and there are several techniques available for generating a pro-ducing cell line. Conventional plasmid transfection is a common method, but for establishing a high producer cell line, gene amplification and time-consuming screen-ings are necessary. An alternative method is the application of BACs as transfection vectors, which generates high producing cell lines without the need for gene amplification. The BAC itself mediates this as it provides a highly transcribed open chromatin region. For this work, two scFc antibodies, 3D6scFc and 2F5scFc, were expressed in CHO cells. Cell lines were established using conventional plasmid transfection and compared to BAC transfectants. Therefore, growth and productivity were continuously monitored. Additionally, qPCR was performed to compare the cell lines regarding gene copy numbers and transcript level. Additionally, intracellular product concentration was determined by flow cytometry. Specific productivities were three to four times higher for BAC transfectants compared to plasmid transfection without amplification. Gene copy numbers and intracellular product concentration were partly higher but transcript levels were significantly increased for BAC transfectants. Thus, BAC transfection demonstrated to be a superior method for establishing stable, high producing CHO cell lines.