Magnetosensitivity in a nosmic Japanese eel Anguilla japonica was examined by conditioning and electrocardiography. Five eels from a freshwater farm in Kagoshima, Japan, were made anosmic by injection of boiling petroleum jelly (130–140°C) into the nasal cavity, a technique widely used in studies on olfaction and olfaction-related behavior of eels. Another five eels were not injected with boiling petroleum jelly and served as controls. Conditioning consisted of exposure of eels to an imposed magnetic field of 192 473 nT. After complete conditioning of the eels, the imposed magnetic field was reduced from 192 473 nT to 12 663 nT during the tests. The control eels showed a significant conditioned response (i.e. slowing of the heart beat) to the magnetic field after one sete of conditioning runs. The anosmic eels did not respond to the magnetic field, presumably due to damage of the olfactory organ from the jelly injection. The results suggest that Japanese eels have a magnetosensitive organ in or around the nares. At 1 month after the anosmia treatment, there was no visible trauma to the olfactory lamellae of anosmic eels.