In 1965, a strange illness, which afterwards was diagnosed as the intoxication caused by organic mercury compounds, began to affect the inhabitants of the riverside areas of the Aganogawa River, Niigata, Japan. The authors have investigated the neurotological disturbances, which occurred in 144 cases intoxicated with organic mercurials. The results obtained are summarized as follows: Recruitment (in SISI and other tests) was negative in all the cases except for 32 with inner ear deafness, and Békèsy’s audiometry (TTS) showed type II: unsettled wide amplitude in 17 cases and severe abnormal adaptation characterizing the type III pattern in nine cases. Spontaneous and positional nystagmus were recorded with ENG in 94 of 144 cases. In 62 of 144 cases, pathological findings of horizontal optokinetic nystagmus were recorded, and those of vertical optokinetic nystagmus were frequently observed in 81 of the 118 cases tested (69 %). Judging from the authors’ observations, neurotological disturbances due to chronic mercurial intoxication may be considered mainly as lesions of the retrocochlea and of the oculomotor system in the brain stem and the cereb