We have studied the spatial expression of the Xenopus GR in early embryos by whole-mount in situ hybridization. At the gastrula stage, GR mRNA is localized in the dorsal ectoderm. By the early neurula stage, GR transcripts were detected along the notoplate. Between mid and late neurula stages, GR mRNA was not detectable. At the tailbud stage, GR mRNA was found in the anterior part of the embryo, including the cement gland, eyes, brain, the foregut, stomodeal-hypophyseal anlage, the olfactory placodes, head mesenchyme and somites. Injection of Xenopus GR RNA into zygotes followed by treatment dexamethasone from the blastula stage onwards inhibits early differentiation. Expression of Xbra, gsc and histone H3 genes in these embryos is not inhibited, indicating that the GR effects are not due to a general squelching effect on transcription.