In the rat superior cervical and coeliac-mesenteric ganglia we have observed three types of small granulated (SG) cell: Type I cells are characterised by membrane-bounded cytoplasmic granules with a core of variable, moderate to low electron-density, whose limiting membranes are rounded in profile ranging from 50-150 nm in diameter. Type II SG cells contain numerous highly electron-dense, polymorphic cytoplasmic granules ranging from 100-300 nm in diameter. The haloes of Type II cell granules are variable in shape, and the core is often eccentrically located or fragmented. Type III SG cells contain membrane-bounded granules with a core of variable moderate to low electron-density. In profile these granules appear oblong or circular with average dimensions of 170 x 50 nm. All three SG cell types receive cholinergic-type pre-ganglionic terminals whose afferent nature is confirmed by their degeneration following pre-ganglionic neurectomy. Only Type I cells have been observed to donate efferent synapses to dendrites of principal ganglionic neurones and are thus interneuronal.