The fine structure of the mouse adrenal cortex was examined with the electron microscope for the presence of neural elements. Several axon terminals containing mostly clear vesicles (60 nm) were noted in the vicinity (250 nm) of the capsular fibroblasts. In the subcapsular region, myelinated as well as unmyelinated fibers were commonly found. Preterminal and terminal axons were also found in close relationship to the parenchymal cells in the zona glomerulosa. Nerve bundles were the most common neural elements in the zona fasciculata. In the zona reticularis axon terminals containing both clear (60 nm) and dense core (120 nm) vesicles were seen in close proximity (30 nm) to parenchymal cells. Although this study did not delineate the type of fibers involved, the axon terminals resemble those of autonomic nerves. This study demonstrates innervation of the mouse adrenal cortex, thus corroborating similar reports by others in different species.