- It is important to identify the mechanisms regulating cardiovascular development. However, complex genetic tools are often required, including transgenic animals that express the lacZ transgene encoding the -galactosidase enzyme under the control of a specific promoter or following recombination with the Cre recombinase. The latter can be useful for identifying specific cell populations of the developing cardiovascular system, including neural crest cells. The tracking of these cells can help clarify their fate in mutant embryos and elucidate the etiology of some congenital cardiovascular birth defects. This chapter highlights the methods used to stain embryonic tissues in whole mount or sections to detect the expression of the lacZ transgene with a focus on tracking cardiac neural crest cells using the Wnt1-Cre and R26R mouse lines. We also provide a protocol using fluorescence-activated cell sorting for collecting neural crest cells for further analysis. These protocols can be used with any embryos expressing Cre and lacZ.