The anatomical localization of beta 1 and beta 2-adrenoceptors was studied in rat lymphoid tissues by quantitative autoradiography using [125I]cyanopindolol as a ligand. In lymph nodes, a significant density of these receptors was found in the medullary cords and the interfollicular cortex, while only low densities were observed in the paracortex. No detectable binding appeared in the remaining areas. In the spleen, these receptors were mainly localized in the capsule, marginal zone of white pulp and red pulp, while the labelling over the white pulp was extremely low. The subtype beta 2 was predominant in both lymph nodes and spleen. The results suggest that beta-adrenoceptors are present in mature cells in lymphoid tissues and are probably not involved in homing mechanisms.