Single crystals of tungsten, grown by decomposition of the chloride in the vapour phase, were investigated. A substructure has been found both with X-ray and microscopic techniques. The disorientation between the subcrystals is at random and is therefore different from that found in single crystals in recrystallized doped tungsten wires. The occurrence of a substructure or even dendritic branches depends upon the circumstances during the growth. The rows of etch pits on the photomicrographs of etched surfaces are of the same nature as those found by other authors on tungsten prepared in a different manner. Electron-microscope pictures of etched surfaces sometimes reveal pyramid shaped etch hills and whisker-like needles, which are supposed to be subcrystals grown with the highest perfection, during temporarily favourable conditions.