The embryonic epidermis of stage 35 Xenopus laevis embryos is a highly differentiated structure composed of four cell types arranged in a regular architecture. Each type is distinguished by its distinct morphological characteristics. Some cells are ciliated (type 1); others have their surfaces covered by abundant, secreted vesicles of 0.1 m diameter (type 2), or multiple linear aggregates of spherical subunits on their apical surfaces (type 3) or large secreted vesicles that emanate from prominent apical holes of 1 m diameter (type 4). In contrast, the macroscopic appearance of embryos exposed to 10 M 1,10phenanthroline (OP) as well as the ultramicroscopic structure and organization of their epidermal cells are markedly altered. The most predominant cells of the embryonic epidermis are undifferentiated and of heterogeneous size. They lack any characteristic morphology and are arranged irregularly. Ghost cells are also identified. The recognizable differentiated cells are decreased in number and present in a scattered arrangement. These are identified as either type 1 or 2 cells but with ciliae that are shorter and thicker than control or with only a few vesicles larger than 0.1 m in diameter on their surface. No cells with linear aggregates or prominent apical holes are identified. Except for the altered epidermis, the embryos do not develop any other major organs and exhibit axial abnormalities with an average dorso-anterior index of three. Thus, the chelating agent OP perturbs metal dependent processes essential for terminal differentiation that may likely account for the resultant abnormalities of embryo organogenesis and morphogenesis.