Neurochemical analysis of norepinephrine and serotonin with high performance liquid chromatography with electrochemical detection (LCEC) in several microdissected central autonomie nuclei of 4 week old and 16 week old spontaneously hypertensive rats (SHR), normotensive Wistar-Kyoto rats (WKY), and control normotensive Wistar rats (WIS), revealed some differences among these strains, but only one change that correlated with the hypertensive state. Norepinephrine levels in the 4 week old SHR were greater in the parabrachial nuclei and the dorsal motor nucleus of X than in the WKY, but levels in the WIS normotensive also were greater than in the WKY, and equalled levels in the SHR. In the 16 week old rats, no difference was noted between NE levels in the SHR and WKY strains, but levels in the locus coeruleus and parabrachial nuclei of the WIS were greater than in both the SHR and WKY. Serotonin levels in the 4 week old SHR and WKY rats did not differ, while levels in the paraventricular nucleus, locus coeruleus, parabrachial nuclei, and medullary raphe nuclei of the WIS rat were greater than one or both of these inbred strains. In die dorsal motor nucleus of X in 16 week old rats, serotonin levels were greater in the SHR than in either the WKY or WIS controls, suggesting one possible transmitter action that should be explored further for its potential relationship to the hypertensive state. These findings demonstrate that norepinephrine and serotonin levels in specific central autonomie nuclei among these strains of rats, with the exception of serotonin levels in the dorsal motor nucleus of X in 16 week old SHR, do not directly coincide with or predict a hypertensive state. We suggest that normotensive control rats other than WKY rats, such as control Wistars, be included in neurochemical studies of monoamines in the SHR and WKY strains to prevent a potential misinterpretation of differences between these inbred strains.