pCMV-LacZ is a mammalian reporter vector designed to expression β-galactosidase in mammalian cells from the human cytomegalovirus immediate early gene promoter (1). pCMV-LacZ contains an intron (splice donor/splice acceptor; 2) and polyadenylation signal from SV40, and the full-length E. coli β-galactosidase gene with eukaryotic translation initiation signals (3). pCMV-LacZ expresses high levels of β-galactosidase and can be used as a reference (control) plasmid when transfecting other reporter gene constructs and can be used to optimize transfection protocols by employing standard assays or stains to assay β-galactosidase activity. Alternatively, the β-galactosidase gene can be excised using the Not I sites at each end to allow other genes to be inserted into the pCMV-LacZ vector backbone for expression in mammalian cells or to insert the β-galactosidase fragment into another expression vector.