The expression of mating behavior in male rats is dependent on estrogen-responsive neurons in the medial preoptic area (MPO). Previous reports showed that mating is attenuated if the aromatization of testosterone to estradiol (E<sub>2</sub>) is blocked in the MPO and that mating is maintained by MPO E<sub>2</sub> implants. However, the mechanisms by which E<sub>2</sub> exerts its action are not fully understood. It had been thought that E<sub>2</sub> acted exclusively by binding to nuclear estrogen receptors to exert it effects; however, recent reports suggest that E<sub>2</sub> also binds to membrane-associated receptors activating downstream intracellular cascade responses. In this study, we aimed to determine if an action of E<sub>2</sub> at the cell surface is sufficient to support mating behavior. Therefore, either vehicle, E<sub>2</sub>, or E<sub>2</sub> conjugated to bovine serum albumin (BSA-E<sub>2</sub>: a complex of E<sub>2</sub> and a large protein that will not cross the plasma membrane, thereby restricting the action of E<sub>2</sub> to cell surface signaling) was chronically administered bilaterally to the MPO of castrated, dihydrotestosterone-treated male rats. Mating behavior was supported by MPO BSA-E<sub>2</sub> implants, suggesting that E<sub>2</sub> operates in the MPO via a cell surface mechanism to facilitate male rat mating behavior.