Using rhodamine-labelled latex beads as a retrograde tracer, we have shown that a subset of the neurons projecting from the lateral thalamic nucleus to the optic tectum of the leopard frog are neuropeptide Y-like immunoreactive (NPY-IR). In juvenile frogs, approximately twice as many lateral thalamic nucleus cells from this area project to the ipsilateral tectum as project to the contralateral tectum. NPY-IR cells make up 25% of the projection to the ipsilateral tectum and 13% of the projection to the contralateral tectum. The ipsilateral NPY-IR projection from the lateral nucleus was present in tadpoles and was similar in its characteristics to that found in the juvenile frog. However, the contralateral tectal projection was virtually nonexistent in these animals. The results of these experiments suggest that NPY from the lateral nucleus is released into the ipsilateral tectal neuropil in both the developing and adult frog.