The aim of this study was to evaluate the accumulation of transition metals in the scalp hair of amyotrophic lateral sclerosis (ALS) patients in the Koza/Kozagawa/Kushimoto (K) area (K-ALS) in the Kii Peninsula, Japan. Metal contents were measured in the unpermed, undyed hair samples of 88 K-residents, 20 controls, 7 K-ALS patients, and 10 sporadic ALS patients using neutron activation analysis at the Research Reactor Institute, Kyoto University. A human hair standard and elemental standards were used as comparative standards. The contents of Zn, Mn, and V were higher, while that of S was lower in K-ALS patients than in the controls. The content of Mn in K-ALS patients negatively correlated with clinical durations. The content of Al was significantly higher in K-residents than in the controls, with 15.9 % of K-residents having high Mn contents over the 75th percentile of the controls. The contents of Zn, Mn, and V were high in the scalp hair of K-ALS patients and correlated with the content of Al. The accumulation of these transition metals may chronically increase metal-induced oxidative stress, which may, in turn, trigger the neuronal degeneration associated with K-ALS.