ABSTRACT The availability of molecular markers now permits the analysis of the common elements of vertebrate gastrulation. While gastrulation appears to be very diverse in the verte brates, by analyzing a head-organizer marker, goosecoid, and a marker common to all forming mesoderm, Brachyury, we attempt to identify homologous structures and equivalent stages in Xenopus, zebrafish, chick and mouse gastrulation. Using a tail-organizer marker, Xnot-2, we also discuss how the late stages of gastrulation lead to the formation of the postanal tail, a structure characteris tic of the chordates.