The Y chromosome gene SRY is the initiator of male sexual differentiation in mammals, but the molecular and cellular mechanisms operating downstream of SRY remain undefined. A deeper understanding of these issues relies on the ability to visualize SRY protein endogenously under a number of experimental conditions. Here we compare the specificity and effectiveness of several available antibodies to mouse SRY. Two antibodies cross-reacted with other SOX proteins in immunofluorescence analyses of transfected cells, and one of these two was unable to detect SRY on Western blots. A third antibody was both avid and specific, and was able to detect endogenous SRY in developing Sertoli cells in mouse genital ridges. Our findings underline the need to distinguish between useful and spurious reagents for biochemical and immunolocalization studies involving mouse SRY protein.