Comparisons between monogamous and promiscuous vole species have proven useful in examining neurobiological mechanisms underlying social attachment. Reward processing is important for social attachment, and the medial prefrontal cortex (mPFC) exerts a direct influence on reward pathways. Dopamine (DA), oxytocin (OT), and arginine vasopressin (AVP) all have been implicated in the regulation of social attachment in monogamous voles. Therefore, we used radiolabeled ligands to examine dopamine D1- and D2-like, OT, and AVP V1a receptor binding densities in the mPFC of monogamous and promiscuous voles. Species differences were found; monogamous voles had higher densities of D2-like and OT receptor binding and lower densities of D1-like and V1a receptor binding than did promiscuous voles. Sex differences also were found; females had higher densities of OT receptor binding but lower densities of V1a receptor binding than did males in both species. Further, the laminar distribution of receptor binding indicates the possibility of an interaction between DA and OT systems in the mPFC in the regulation of social attachment. Differences in D1- and D2-like receptor binding between species are discussed in terms of how they might modulate cortical activity and subsequent DA release in the nucleus accumbens (NAcc).