Diphenylarsinic acid poisoning from chemical weapons in Kamisu, Japan.

We noted a new clinical syndrome with prominent cerebellar symptoms in apartment building residents in Kamisu, Japan. The well that provided drinking water contained diphenylarsinic acid, a degradation product of diphenylcyanoarsine or diphenylchloroarsine, which were developed for use as chemical weapons, inducing severe vomiting and sneezing. Characteristics of diphenylarsinic acid poisoning include brainstem-cerebellar and cerebral symptoms. Mental retardation associated with brain atrophy in magnetic resonance images was evident in some infants. We must be vigilant to prevent or minimize the effects of further diphenylarsinic acid poisoning in Japan or elsewhere.