A cold lesion was produced in the mouse parietal cortex. The damaged area was examined for alterations in the catecholamine fibres either by fluorescence microscopy or by electron microscopy. Within 24 h of injury many damaged catecholaminergic nerves were observed in close association with small intracerebral blood vessels. This relationship between nerves and blood vessels was not apparent in the control cortex. In the electron microscope, swollen non-myelinated axons containing an accumulation of dense-cored vesicles were observed close to the vessel wall but separated from it by astrocytic process. Six days after injury regenerating catecholaminergic nerve fibres were found close to immature capillaries. Axonal-like profiles containing dense-cored vesicles were observed adjacent to the endothelial call basement membrane. The number of regenerating nerves declined with time and the only fluorescent catecholaminergic nerves that remained 12 weeks after injury were in an area known to be rich in capillaries.