Dopamine exerts a robust promoting effect on adult neurogenesis. Here, we report the presence of an intense dopamine (tyrosine hydroxylase immunoreactive) zone along the ventricular border of the caudate nucleus in patients with Huntington's disease, but not in age-matched controls. This thin (150-400 microm) paraventricular zone was composed of numerous small and densely packed dopamine axon varicosities and overlapped the deep layers of the subventricular zone. Immunoreactivity in the paraventricular zone was 50% higher than in adjacent striatal areas. This intense dopamine zone concurs with the striking increase of neurogenesis noted in the subventricular zone of Huntington's disease patients and indicates that dopamine might play a crucial role in intrinsic mechanisms designed to compensate for the massive striatal neuronal losses that occur in Huntington's disease.