Endogenous alcohol has been applied for spontaneous ethanol production via different metabolic pathways of the human body. Auto-brewery syndrome describes the patients with alcohol intoxication after ingesting carbohydrate-rich meals. The main objective of this study is to investigate the effect of diabetes mellitus (DM), liver cirrhosis (LC) and presence of both (DM and LC) on blood alcohol concentration (BAC) especially after carbohydrate ingestion. BAC has been measured by headspace gas chromatography-mass spectrometry in three groups of humans namely control, DM, LC and both (DM and LC) groups. The results showed that BAC in control group was 0.01-.3 mg/dL with mean 0.3 +/- 0.41 mg/dL. In patients with DM, BAC is significantly higher than that of control group 4.85 +/- 3.96 mg/dL. In patients with LC, BAC was 3.45 +/- 2.65 mg/dL. In patients with both DM and LC, BAC increases to reach 10.88 +/- 5.36 mg/dL. Endogenous ethanol production appears to increase in DM and LC. Also, it increased much more in patients with both diseases, but it did not reach toxic levels. On comparing BAC and blood glucose level in each group, all groups show insignificant correlations (p >0.05).