Selective, 35S-labeled, oligonucleotide probes were designed from sequences of the rat beta-1 and beta-2 adrenoceptor messenger RNAs for use in situ hybridization experiments on sections of unfixed rat brain and spinal cord. After hybridized sections were exposed to film or dipped in autoradiographic emulsion, specific and selective labeling patterns characteristic for each receptor messenger RNA and region of the central nervous system were observed. For example, labeling for beta-1 messenger RNA was found in the anterior olfactory nucleus, cerebral cortex, lateral intermediate septal nucleus, reticular thalamic nucleus, oculomotor complex, vestibular nuclei, deep cerebellar nuclei, trapezoid nucleus, abducens nucleus, ventrolateral pontine and medullary reticular formations, the intermediate gray matter of the spinal cord and in the pineal gland, while beta-2 messenger RNA labeling was strongest in the olfactory bulb, piriform cortex, hippocampal formation, thalamic intralaminar nuclei and cerebellar cortex. In some of these regions the beta-1 labeling seemed mainly confined to the cell nucleus. Whether or not this apparently nuclear labeling is specific, i.e. indicates synthesis of beta-1 receptor, remains to be established. However, all labeling patterns described disappeared when excess unlabeled probes were added to their respective radiolabeled probes or when sense probes were employed. Since the in situ method labels only cell bodies that produce the messenger RNA for these two beta receptor subtypes, a comparison between these maps and those of past autoradiographic studies mapping the location of central beta receptors using drugs as radioligands may produce further insights regarding the pre- and postsynaptic localization of these receptors in the various parts of the central nervous system circuitry.