High-voltage electron microscopic observations have been performed on intraglomerular dendritic branches of mitral and tufted cells and spines of granule cells in the Golgi-impregnated mouse olfactory bulb. The observations revealed that intraglomerular tufts of mitral and tufted cells have a very similar structure consisting of four morphologically distinct parts: (i) thick, smoothly outlined proximal parts; (ii) relatively thick varicose parts; (iii) very thin varicose parts, which form terminal branches; and (iv) spine-like small appendages. Granule cell spines in the external plexiform and mitral body layer have terminal swellings of various shapes and sizes, whose width is between 0.4 and 1.5 microns. Spines in the granule cell layer usually have swellings smaller than 0.4 micron in width. In addition, the density of spines per proximal 10 microns length of a deep dendritic trunk was estimated in 10 granule cells and proved to vary greatly from cell to cell--from 7 to 28 spines.