AbstractThe morphology of the hypothalamo‐hypophyseal tract of 35 hibernating bats (Myotis lucifugus lucifugus) was studied in chrome‐alum‐hematoxylin‐phloxine‐stained serial coronal and sagittal sections. Vinyl acetate and wax‐plate reconstructions also aided in describing the two neurosecretory hypothalamic nuclei of this system. The most prominently defined nucleus, the supraoptic, consisted of a smaller portion rostral to the optic tract that was tenuously connected to a larger caudal portion. The probability that some of the posteriorly located cells of the caudal portion represent other hypothalamic nuclei is discussed. The shape and location of the paraventricular nucleus was more difficult to determine. Although the neurosecretory cells of this nucleus were similar in their irregular or eliptical shape to those of the supraoptic nucleus, the majority of the paraventricular cells were smaller and had less of an affinity for the chrome‐alum‐hematoxylin stain.The majority of CHP‐positive axons originating in the supraoptic nucleus converged toward the median eminence and terminated in the pars nervosa. Most of the axons from the paraventricular nucleus coursed laterally toward the supraoptic nucleus where they followed the pathway described from this nucleus. The localization of CHP‐positive material in the neurohypophysis is presented. Comparisons were made between the morphology of this system in the hibernating bat and that of other species of mammals reporte