Ethanol (0.3 g/kg) was administered intravenously to adult, male rats at 3 h or at 1 and 3 h after gastric intubation of 7 mg/kg calcium carbimide (CC). For animals administered CC and two ethanol doses, blood ethanol concentration was similar for the two doses; however, blood acetaldehyde concentration was significantly less for the second ethanol dose compared with the first dose as determined by the area-under-curve data. Hepatic aldehyde dehydrogenase activity was determined over the 3.5- to 5-h interval after CC pretreatment. The inhibition of low Km and high Km aldehyde dehydrogenase activity in liver homogenate and in hepatic mitochondrial, cytosolic, and microsomal fractions was significantly less for rats administered CC followed by two ethanol doses compared with that for animals administered CC alone or CC followed by one ethanol dose. The data demonstrate that increased acetaldehyde concentration, produced during the CC - ethanol interaction, can augment the recovery of hepatic aldehyde dehydrogenase activity following CC pretreatment and indicate the existence of a displaceable enzyme inhibitor derived from CC.