Efferent connections of medial (nucleus cuneiformis) and lateral regions of the midbrain reticular formation (MRF) were investigated using an anterograde autoradiographic technique in cats. Efferent fibers from the MRF ascend to the globus pallidus, substantia innominata, hypothalamus, subthalamus, and nonspecific associative and relay nuclei of the thalamus. Descending pathways to the conclusion that the cuneiform nucleus is more of a nonspecific structure than an association auditory center. The lateral reticular region had numerous projections to the lateral geniculate body and, together with the parabigeminal nucleus, forms the midbrain visual complex.