Regional differences of proteins were studied by two-dimensional gel electrophoresis in early embryos of Xenopus laevis. Pairs of blastomeres on the dorso-ventral axis were isolated from 16- and 32-cell embryos. Some dorso-ventral differences have been detected at 32-cell embryos. The proteins which were clearly detectable in the vegetal cells of the ventral marginal zone were only faintly detectable or undetectable in those of the dorsal marginal zone, and a regionally specific spot was detected in dorsal blastomeres.