The projection from nucleus isthmi (NI) to the optic tectum (OT) was investigated in the goldfish, Carassius auratus, by retrograde transport of biocytin applied at various sites in a tectal lobe. In previous studies, this projection is described as predominantly from the ipsilateral NI and maps topographically along the approximate rostrocaudal axis of both brain areas. However, the rostromedial tectal lobe, the tectal region representing the binocular visual field, receives afferents from both the ipsilateral and the contralateral NI. The contralateral isthmic neurons are found at the most caudal position in NI and are not topographic with the tectum. The bilateral projection from NI to the tectum may play a role in functions requiring the coordination of both eyes.