Intragastric or intraperitoneal ethanol (EtOH) treatment inhibits reproductive functions in females and male rats. The area of the hypothalamus where these effects take place is unknown. As the participations of the preoptic-anterior hypothalamic area (POA-AHA) in regulating ovulation is asymmetric, this study aims to analyze the effects on 17β-estradiol(E2 ), progesterone, luteinizing hormone (LH), follicle-stimulating hormone (FSH) serum levels, the messenger ribonucleic acid (mRNA) expression of estrogen receptor alpha (ERα) and beta (ERβ), and ovulation resulting from unilaterally microinjecting water or an EtOH solution into either side of the POA-AHA. The treatment consisted of microinjecting a 8.6 μM EtOH solution into either side of the POA-AHA. The study was performed on groups of adult cyclic rats at 09.00 hours on diestrus-1, and sacrificed on diestrus-2 at 13.00, on proestrus at 09.00 or 17.00 or on estrus at 09.00 hours. Ovulation rates were assessed in rats sacrificed on estrus. Hormonal serum levels were measured using radioimmunoassay, and as a function of ERα and ERβ mRNA expression in each side of the POA-AHA by reverse transcriptase polymerase chain reaction. EtOH treatment blocked ovulation and the preovulatory release of LH, and lowered E2 levels. Irrespective of the treated POA-AHA side, ERα mRNA expression was consistently lower in the left POA-AHA and higher on the right. EtOH treatment in the left POA-AHA decreased FSH serum levels and lowered ERβ mRNA expression. In turn, EtOH treatment on the right POA-AHA resulted in higher FSH levels and ERβ mRNA expression. The present results show that EtOH blocks the preovulatory surge of LH on the POA-AHA. The effects of EtOH treatment of preovulatory FSH surge on the POA-AHA are asymmetric (stimulative on the right and inhibiting in the left). The effects of EtOH treatment on preovulatory LH and FSH surge could be explained by the inhibition of ERα and ERβ mRNA expression, respectively.