The transfection of well-differentiated sensitive cells requires careful optimization of the conditions used. In addition to the transfection method chosen, the amount of cells plated, and thus the density of the cells, as well as the influence of the serum concentration play a critical role in the case of LNCaP cells. We also found out that the only appropriate control plasmid for the transfection efficiency was pCMV beta-gal driven by the cytomegalovirus promoter.