Studies show that estrogens can influence alcohol consumption; however, findings are variable and an etiology remains unknown. Furthermore, estrogen administration can alter several neurotransmitter systems implicated in alcohol consumption, including the beta-endorphin (beta-EP) system. The present studies investigate (a) whether estradiol valerate (EV) alters voluntary alcohol consumption in Wistar and Lewis rats, (b) if an effect of EV on drinking is associated with changes in hypothalamic or pituitary beta-EP content, and (c) whether differences in alcohol drinking between treatment and rat groups are related to locomotor or defensive behavior/anxiety scores. Of 30 Wistar and 30 Lewis rats used in this study, half were injected with 2 mg EV in 0.2 ml sesame oil, while the remainder were injected with the vehicle only. After 8 weeks, all animals were tested in the open field and elevated plus maze. A week later, 4-6 animals in each group were sacrificed. The remaining animals were tested for voluntary alcohol drinking for 24 days prior to being sacrificed on the last day. Radioimmunoassay was used to estimate hypothalamic and pituitary beta-EP content. Wistar and Lewis rats injected with EV showed an increase in alcohol drinking, but their behavior scores and beta-EP levels remained unaltered. This result suggests that any EV effect on drinking is unrelated to changes in beta-EP or behavioral performance. Furthermore, Wistar rats show higher alcohol drinking, locomotor and defensive behavior scores, and hypothalamic beta-EP than Lewis rats. Higher alcohol drinking by Wistar rats might be due to higher behavioral scores or endogenous opioid activity/sensitivity.