Differential intracellular formation of indophenol with very low concs. of reagents and differential reduction and reoxidation of indophenol, methylene blue and Janus green, all in living, intact embryos, show very similar oxidation-reduction patterns in the urodele, Triturus, and the teleost, Oryzias latipes. In early stages oxidation-reduction is most rapid in the apical (animal) polar region but soon becomes more rapid on the presumably dorsal than on the other side. During gastrulation oxidation-reduction becomes more rapid in the dorsal lip than elsewhere. With amphibian neurulation, and preceding teleost head formation, this pattern is replaced, except for a short gradient in the tail bud, by a gradient with future head as the high region, and from this stage on oxidation and reduction progress from the head posteriorly and from dorsal region ventrally. This gradient pattern persists in the developing amphibian leg and the teleost optic vesicle and cup.