Afferent subcortical connections to the proreal gyrus of the prefrontal cortex (PFC) in the dog were investigated using the horseradish peroxidase retrograde transport method. The afferent projections derive mainly from dorsal-intermediate and caudal regions of the mediodorsal nucleus (MD), from $he ventral as well as from the lateral thalamic nuclei. In the ventral nuclei, the distribution of labeled cells showed a topography correlated with injections localized in the anteroposterior direction. Furthermore, single cells were labeled in midline and intralaminar thalamic nuclei as well as some extrathalamic structures. The data obtained in behavioral and anatomical experiments with dog and monkey are discussed. The distribution of afferent projection from MD and the functional division on particular subfields of PFC seems to be in accordance in both species.