Neuropeptides have now been localized throughout the nervous system. This talk focuses attention on (1) the interplay of peptides and other neurotransmitter systems in the hypothalamus - median eminence - pituitary gland. The multiplicity of neurochemicals is perceived to be responsible for the integrated control of pituitary hormone releasing factors; (2) the role of neuropeptides in the regulation of cardiovascular function in the hypothalamus-preoptic area. We investigated the effects of discrete intrahypothalamic injections of a variety of peptides on blood pressure and heart rate. We concluded that neuropeptides have a diversity of central cardiovascular actions and that not all areas containing a given peptide respond with cardiovascular change when the peptide is injected. Also, peptide specific actions originating within the same nucleus have been demonstrated, and the same peptide may have different vascular effects in different segments of the same nucleus; (3) the colocalization of neuropeptides with other classical neurotransmitters. We have found modulatory behavioral effects (“boxing”) of combinations of transmitters and peptides injected into the postsynaptic site in the brain.