In a dynamic inhalation system, mice, rats and rabbits were exposed to bromobenzene vapour (250-3400 p.p.m.) for 4 hr. Blood concentrations of bromobenzene were determined by head-space gas chromatography. After inhalation of 1000 p.p.m. for 4 hr, concentrations of 153, 102 and 47 micrograms bromobenzene/ml blood were found in mice, rats and rabbits, respectively. In vitro experiments showed a blood/air partition coefficient at 37 degrees of approximately 200, which was reflected by a linear uptake of bromobenzene up to an air concentration of 2500 p.p.m. Compared with results obtained previously by intraperitoneal bromobenzene administration inhalation resulted in higher blood concentrations.