The effects of inhalation exposure of rats methyl bromide (MB) on dopamine (DA), homovanillic acid (HVA), norepinephrine (NE), 3-methoxy-4-hydroxyphenylglycol (MHPG), serotonin (5HT), and 5-hydroxyindoleacetic acid (5HIAA) concentrations of various brain regions (striatum, hypothalamus, frontal cortex, midbrain, and medulla oblongata) were investigated. Rats received a single 8 hr exposure to MB, and amines and metabolites were separated by a reverse-phase HPLC, and were quantified via native fluorescence. An exposure to 100 ppm MB decreased tissue levels of DA and NE in all brain areas at 0 or 2 hr following exposure. HVA and MHPG contents were significantly increased in almost all brain regions. In a second study, rats were exposed to four concentrations of MB ranging from 31-250 ppm, and monoamine and metabolite levels in brain regions measured immediately after the exposure. Again, there were dose-dependent decreases of DA and NE, and increases in HVA and MHPG. Less clear changes in 5 HT and 5HIAA contents were observed. These data suggest that alterations of catecholamine metabolism may be a factor in MB-induced neurotoxicity.