Benzo[alpha]pyrene (B[a]P) is a product derived from incomplete combustion of organic material and is considered responsible for chemically-induced cancer in humans. In the present study, the levels of noradrenaline (NA), dopamine (DA), dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), 5-hydroxytryptamine (5-HT), and 5-hydroxyindoleacetic acid (5-HIAA) were measured in the brains of female Wistar rats 6, 12, 24 and 96 h after a single dose of B[alpha]P (50 mg kg(-1) b.w., i.p.), and also after repeated administration of B[alpha]P (50 mg kg(-1) b.w., i.p., 2 x wk, 1 mo). The brain regions studied were the striatum, hypothalamus, midbrain and cortex. Catecholamines were measured using high performance liquid chromatography (HPLC) and electrochemical detection. Significant changes were observed in the striatum where NA, DA, DOPAC were decreased after 24 h and HVA was decreased after 6 h. In contrast, no major alterations occurred in 5-HT and 5- HIAA. In the hypothalamus, a significant decrease in NA was observed after 96 h. In the midbrain, the most important change observed was the decrease in NA after 24 h. A trend toward an increase in 5-HIAA was observed in the cortex after 6 h. The results demonstrate that B[alpha]P induces alterations in the dopaminergic and serotoninergic systems throughout the brain. These alterations may lead to behavioural and hormonal disturbances.