A fraction enriched in dendro-dendritic synaptosomes was isolated from rat olfactory bulb by a rapid method. Synaptosomes preserved their ultrastructure and showed configurational changes in relation to incubation in physiological ion medium as described earlier in the case of cortical synaptosomes. Dendro-dendritic synaptosomes were larger and contained more mitochondria than cortical synaptosomes. Doublets of terminals synapsing with each other were frequently seen and each terminal contained synaptic vesicles. Oxygen consumption of dendro-dendritic synaptosomes was decreased by ouabain and increased by 2,4-dinitrophenol. High-potassium medium evoked a considerable release of GABA and dopamine but not of noradrenaline or serotonin in accordance with histochemical published data.