The present investigation deals with in vivo binding of 3H-corticosterone in the brains of tree shrews as visualized by autoradiography. Tree shrews were injected with 3H-corticosterone and brain sections were mounted on slides which were subsequently exposed on tritium sensitive film. The relative labeling of 20 different brain structures was determined densitometrically. The indusium griseum, which demonstrated the highest binding for corticosterone of all brain regions in the autoradiograms, was taken as reference and defined as 100% relative labeling (RL). As in other species, the hippocampal subdivisions of the tree shrew retained high amounts of the steroid (60 to 80% RL). In other parts of the limbic system, medium labeling intensities were observed with approximately 40% RL in the lateral septum. The amygdala was less intensely labeled revealing around 30% RL in the basal accessory, the cortical, central, and the lateral nuclei. Autoradiographic grey values in the ventral striatum and pallidum were comparable to those in the amygdala, but in the islands of Callejae they were approximately as high as in the lateral septum (44% RL). In contrast to previous reports dealing with other species, the tree shrew cerebellum also demonstrated a high binding capacity for corticosterone. The RL was nearly 60% in the cerebellar granular layer. This finding may indicate that the cerebellum also plays a role in mediating the effects of corticosterone in the central nervous system.