The effects of alcohol on the availability of oxygen within the uterine lumen of rats were determined on Day 4 of pseudopregnancy. Intraluminal oxygen tension (pO2) was measured in vivo in anesthetized rats using a 22-gauge polarographic oxygen sensor. Intrauterine pO2 was measured for 15 min before and after intravenous injection of alcohol (1.0 g/kg: 100% ethanol/saline, 1:2v/v) or vehicle (physiological saline). Alcohol administration increased mean intrauterine pO2 (mm Hg) from a pretreatment level of 28.3 +/- 2.8 to 38.7 +/- 3.8 mm Hg (p less than 0.05, n = 10) at 15 min postinjection. The rapid rise in oxygen tension was accompanied by increased frequency of fluctuation (peaks/hr) in intraluminal pO2 (prealcohol: 64.2 +/- 8.8 vs. postalcohol 96.0 +/- 7.7 peaks/hr; (p less than 0.05, n = 10). Injection of saline did not alter any aspect of intrauterine pO2. During the period of measurement of luminal pO2, blood alcohol levels increased from 0 during pretreatment to 106 mg% within 10 min of injection. These results indicate that alcohol increases the availability of oxygen within the uterus during the time of endometrial sensitivity to deciduogenic stimuli and blastocyst implantation.