Pregnant female rats, challenged with a single ethanol dose near the mid‐gestation period, displayed a significant circadian variation in the rates of both blood ethanol clearance and ethanol metabolism. Maximal rates occurred near the dark‐to‐light change of the LD 12:12 regimen. These rhythms may have been synchronized by pregnancy‐induced hormonal cycling since these same animals, challenged as virgins with asynchronous estrus cycling, showed no difference in ethanol metabolic rate over the 24‐h span and circadian variation in blood ethanol clearance rates of questionable significance.