The effect of 1-butyl-biguanide and glibenclamide on the ethanol absorption in the rat gastrointestinal tract has been investigated. Oral administration of biguanide (100 mg/kg) inhibited the appearance of ethanol in the blood following oral ethanol loading. Glibenclamide (10 mg/kg) did not induce any alteration in the blood alcohol concentration as compared with the control's level. Oral biguanide pretreatment did not induce any change in the blood alcohol concentration when ethanol was given i.v. We conclude that 1-butyl-biguanide does exert an inhibitory effect on the absorption of ethyl alcohol in vivo in the rat.