pIRES2-DsRed-Express contains the internal ribosome entry site (IRES; 1, 2) of the encephalomyocarditis virus (ECMV) between the MCS and a mutant of the Discosoma sp. red fluorescent protein DsRed-Express coding region (3–5). This permits both the gene of interest (cloned into the MCS) and the DsRed-Express gene to be translated from a single bicistronic mRNA. pIRES2-DsRed-Express is designed for the efficient selection by flow cytometry of transiently transfected mammalian cells expressing DsRed-Express and the protein of interest. This vector can also be used to express DsRed-Express alone or to obtain stably transfected cell lines without timeconsuming drug and clonal selection.