Movement of brominated benzenes in rats and mice was investigated. The concentration of o-dibromobenzene in several tissues and organs reached the highest value within 10 hours of a single oral administration and then decreased rapidly. The accumulation of o-dibromobenzene in tissues and organs was in the descending order of adipose tissue, liver (=pectoral muscle), kidney, brain and blood. A similar tendency was observed in mono-and tribromobenzene administered animals. The concentration of hexabromobenzene following continuous intraperitoneal administration reached the highest value 16.3 (liver) to 28.8 days (brain) after the administration. The biological half life of hexabromobenzene ranged from 2.0 (kidney) to 4.1 days (brain) in the first phase of excretion, and from 5.2 (kidney) to 7.3 days (adipose tissue) in the second phase of excretion. Accumulation of hepatic triglyceride due to administration of brominated benzenes occurred. A decrease in the percentage of arachidonic acid among total fatty acids was observed after the administration of brominated benzenes. It is suggested that accumulativeness of brominated benzenes becomes higher with the number of bromine atoms. Clonic toxicity induced by these compounds needs to be investigated in this connection.