Cadmium poisoning has been known to result in olfactory dysfunction like anosmia, but the morphological aspect of the olfactory impairment has not been investigated. This study was designed to observe morphologic changes of the olfactory bulb induced by cadmium poisoning in the rat. The experimental rats were given daily subcutaneous injection of 0.1% solution of cadmium chloride(1.7mg/kg) for 3 weeks. The control group was injected with the same volume of normal saline solution. The control and experimental animals were sacrificed 8 hours after the last injection. The olfactory bulbs were fixed with phosphate-buffered 2.5% glutaraldehyde-2% paraformaldehyde through cardiac perfusion. The olfactory bulbs were removed, postfixed in osmium tetroxide, dehydrated and embedded in Epon 812. The ultrathin sections were stained with uranyl acetate and lead citrate, and subjected to transmission electron microscopic examination. The results were as follows : 1) In the glomerular layer of olfactory bulb, the axons of olfactory cells showed multiple electron-dense bodies which were thought to be phagolysosome. The dendrites which formed synapse with the axons revealed no abnormality. 2) In the other layers of olfactory bulb including the external plexiform layer, the mitral body layer and granule layer, no ultrastructural abnormality was found. The above findings suggest that cadmium poisoning may cause selective damage to the axons of the olfactory cells in the bulb and the damaged organelles may induce the formation of phagolysosomes by autophagy. It is inferred that cadmium-induced anosmia is probably due to the selective damage of olfactory cell axons.