The NADPH oxidases, originally known to be responsible for the respiratory burst in phagocytes have been shown to be expressed and functionally active in the heart, vasculature and many other organs. In addition to p22phox, the core proteins NOX1-4 as well as DUOX1-2, and the regulatory components p47phox, p67phox, NOXO1, NOXA1 and DUOXA1-2 have been described. This family of enzymes shares the capacity to generate superoxide or H₂O₂ and has been implicated in many physiological and pathophysiologial functions. However, their possible implications during embryological development are unknown. We evaluated the expression pattern of NADPH oxidase components during the embryological development in post-implantation stages, until embryological organogenesis.A RT-PCR analysis of E7.5 to E10.5 embryos showed expression of p22phox, p40phox, p47phox and p67phox subunits in all stages. In contrast, NOX homologs presented a temporal pattern. Whereas Nox1 was expressed in all stages and NOX2 and NOX4 were detected from E8.5 on with the onset of hematopoiesis, NOX3 was not expressed. Similarly, DUOX2, and DUOXA1-2 were expressed in all stages, whereas DUOX1 expression was strong at E7.5, but decreased afterwards. In situ hybridization analysis showed localization of the p22phox transcripts in primordial endoderm, foregut area and extra-embryonic ectoderm of E7.5 embryos which was there after extended to chorion, amnion and neural ectoderm. Upon onset of vasculogenesis at E8.5, p22phox was expressed in the yolk sac and primordial heart, p67phox in the yolk sac and whole embryo and NOXO1 only in embryonic tissues. Later, p22phox mRNAs were localized to the areas of organogenesis, the ventral mesoderm, the limb buds and the branchial arches, similar to p40phox, p47phox, p67phox, NOX2 and NOX4. Furthermore, the presence of ROS was analyzed by dihydroethidium (DHE) staining on serial cryo-sections. Thus whole E8.5 embryos showed high ROS levels in yolk sac and extraembryonnic tissues as allantois, and whereas ROS production was found in the whole embryo at E10.5. These findings showed a sequential expression of the NOX components during embryological development with a suggested function for NOX1, DUOX1 and DUOX2 in early embryological development and also later in migration and differentiation processes. The different expression patterns suggest that NADPH oxidase subunits have differential functions in extra-embryonic versus embryonic development and organogenesis.