Detailed quantitative studies have demonstrated a topographical heterogeneity of nerve fibre densities in the cerebral arteries at the base of the brain as well as local changes in ageing and Alzheimer's patients. In this study, we test the hypothesis that local patterns of innervation are influenced by changes in flow fluctuations. This was investigated by inducing chronic anosmia and monitoring the nerve fibre density in the basal cerebral arteries in the adult rat. The olfactory epithelium was examined after staining with hematoxylin and eosin and showed a marked reduction of thickness in the anosmic group compared to the control group. The olfactory bulb was histochemically stained for succinate dehydrogenase (SDH) activity and showed a reduced staining in the anosmic group compared to the controls. Whole mount preparations of the basal cerebral arteries were immunostained for the general neural marker protein gene product (PGP) 9.5. The nerve fibre densities of the vessel walls were quantified by image analysis and expressed as area percentage and intercept density. This analysis showed a significant reduction in area percentage for the first part of the anterior cerebral artery, as well as for the second part of the anterior cerebral artery, and a significant reduction in intercept density for the second part of the anterior cerebral artery in the anosmic group. We conclude that peripherally induced anosmia decreases nerve fibre density in the anterior cerebral artery that may be due to a decreased metabolic activity in the rhinencephalon and, as a consequence, a reduction of flow fluctuations in the blood vessels supplying this area occurs.