Four male alcoholic volunteers ingested two doses of 0.4 g/kg ethanol at 10h and 13.25 h after oral administration of 0.7 mg/kg calcium carbimide (CC). The interaction consisted of increases in blood acetaldehyde concentration and heart rate. For all the subjects, the magnitude of increased blood acetaldehyde concentration was less for the second ethanol dose, and for three individuals, the heart rate increase was less for the second ethanol dose. In the second study, one subject ingested 0.4 g/kg ethanol at 12h after oral administration of 0.7 mg/kg CC in three, separate, experimental sessions. For the interaction, there was large intraindividual variability in the increased blood acetaldehyde concentration, and small variability in the increased heart rate. There were significant, positive linear correlations between blood acetaldehyde concentration and heart rate for two of the three experiments, and there was appreciable variability in the slopes of the regression lines. The results indicate that under the conditions of these studies, the intensity of the CC-ethanol interaction experienced by an individual could be reduced for the ingestion of a second dose of ethanol during the same drinking session. Furthermore, there could be appreciable intraindividual variability in the intensity of the interaction from one drinking session to the next.