The delivery of foreign DNA into eukaryotic cells is one of the most common molecular biology techniques to study biological mechanisms. However, unlike transformed cell lines, the efficient transfection of primary cells can be a problem. EpiFectagen II is a cationic polymer-based transfection system specifically designed and optimized for efficient transfection of primary epithelial cells cultured in serum-free medium, such as Human Esophageal Epithelial Cells, Bronchial Epithelial Cells, Tracheal Epithelial Cells, Small Airway Epithelial Cells, Prostate Epithelial Cells, Corneal Epithelial Cells, Ovarian Surface Epithelial Cells and Mammary Epithelial Cells. Transfection with EpiFectagen II can be carried out in the presence of antibiotics. Instead of normal two-day transfection, an optimized one-day transfection procedure can be performed for time-saving and highly reproducible transfection.