Bismuth is used for a multitude of industrial purposes and has partly replaced toxic heavy metals such as lead and mercury in e.g. lubricants and shotgun pellets. In medicine, bismuth-compounds have long been used to remedy gastrointestinal disorders; lately in combination with antibiotics to treat Helicobacter pylori associated peptic ulcers. An epidemic episode of bismuth-induced encephalopathy in France in the 1970s revealed the neurotoxic potential of bismuth. This incidence, involving almost 1000 patients, remains unexplained and the contribution of other factors besides bismuth has been postulated. Recently an autometallographic technique made it possible to detect bismuth in morphologically intact tissue. In the present study, autometallographicly detectable bismuth was seen throughout the brain following intraperitoneal and intracranial exposure. The neuronal staining pattern seems highly organized with some areas heavily stained and others with low or no staining. Long-term (8 months) intraperitoneal exposure led to higher bismuth uptake than short-term (2 weeks) exposure. Following both intraperitoneal and intracranial exposure, high amounts of bismuth were found in the reticular and hypothalamic nuclei, in the oculomotor and hypoglossal nuclei and in Purkinje cells. Within the central nervous system (CNS) retrograde axonal transport was seen after intracranial bismuth exposure. Axonal transport seems to influence the distribution of bismuth as the highest uptake of bismuth after intraperitoneal exposure was seen in the facial and the trigeminal motor nuclei, i.e. neurones with processes outside the blood-brain barrier, whereas these nuclei contained no bismuth following ic exposure. Ultrastructurally, accumulation of bismuth was seen in lysosomes.