The island of Euboea lies along the SE coast of the mainland of Greece. Structurally it belongs to the Pelagonian zone. In the litterature there are two opposing hypotheses to explain the origin and emplacement of the ophiolites: 1) A Pelagonian micro-continent separated an internal oceanic basin from an external one. Following this hypothesis the ophiolites were derived from the external basin. 2) A single ocean (Tethys) existed and was located in what is now the Vardar zone. In this case the ophiolites, including those of Euboea, were thrust from the NE towards the SW. According to most authors a chaotic assemblage ("diabase-chert formation", etc.) has been described lying on top of a continental "basement" of Jurassic limestones. During Upper Jurassic- Lower Cretaceous times this chaotic assemblage was overthrust by a nappe composed mainly of peridotites and serpentinites. The higher members of this ophiolitic sequence, gabbros, diabases, etc., are thought to have been eroded before the transgression of Upper Cretaceous limestones. In the region studied, such a succession is not obvious in the field. Four sections are described, three of which contain good zones of rodingites. The rock enclosing the rodingites is a peridotite, usually highly or completely serpentinized. From a study of the relics of primary minerals the original peridotite appears to have been a harzburgite tectonite with lherzolitic affinities. The rodingites occur either in lenses, as dikes or in zones of differentiation. They are derived from diabases or gabbros (either in dikes or differentiated gabbroic zones). Except in a few rare cases a great development of calc-silicates is observed in these rodingites. The only important original mineral which is more or less preserved is pyroxene. Garnet is the most developed calc-silicate. The lattice spacing "a" varies between 11,883 Å and 12,072 Å, indicating a range in composition from an almost non-hydrated grossular to a completely hydrated one. Other calc-silicates include prehnite, clinozoisite, zoisite, xonotlite and vesuvianite. In some specimens calcite also seems to have taken part in the process of rodingitization. In addition to being replaced by garnet, the pyroxene often alters to actinolite-tremolite. Generally speaking, the chloritized zones near the contact with the enclosing serpentinite are either very poorly or not developed at all. Some examples of slightly or partially rodingitized gabbroic rocks are illustrated to show that some of the rodingites described could have such an origin.