The bacterial lacZ gene is widely used as a reporter in a myriad of mouse transgenic experiments. beta-Galactosidase, encoded by lacZ, is usually detected using X-gal in combination with ferric and ferrous ions. This assay produces a blue indole precipitate that is easy to detect visually. Here, we show that Salmon-gal in combination with tetrazolium salts provides a more sensitive and faster staining reaction than the traditional beta-galactosidase assay in mouse embryos. Using a combination of Salmon-gal and tetranitroblue tetrazolium, we were able to visualize the activity of beta-galactosidase in embryos at stages when the customary X-gal reaction failed to detect staining. Our studies provide an enhanced alternative for beta-galactosidase detection in expression and cell fate studies that use lacZ-based transgenic mouse lines.