The elucidation of neuronal circuitry has been a major goal in the neurosciences. Anatomic studies with radioactive amino acids and other neuronally transported substances such as horseradish peroxidase have focused on possible relationships among different cell body groups in the central nervous system. In most of these experiments, however, neurochemical features of the relevant neural regions are usually not considered. Yet immense interest in certain of these neurochemicals exists, especially transmitters and related substances involved in neuronal communication processes, because of their obvious or apparent significance for functional neurobiology. In the present report we attempt to address the problem of transmitter neuroanatomy in three regions of the brain thought to be involved in cholinergic-monoaminergic interactions: the substantia nigra, corpus striatum and locus ceruleus.