The word “endogenous” means produced or originating from within the body, so endogenous ethanol therefore implies a spontaneous auto regulation of ethanol through various human metabolic processes. In the current research, endogenous ethanol concentrations in blood were determined by sensitive headspace gas chromatography/mass Spectrophotometry in 1400 residents of Saudi Arabia. The subjects were from 14 nationalities, of both sexes and of different age groups. There was no significance difference in blood ethanol concentration between nationalities or between sexes within and between nationalities. The data was extracted and the overall mean ± SD, minimum, maximum, 5% percentile and 95% percentile were 0.14, ± 0.35, 0.00, 1.53 , 0.00, 1.20 mg/dl respectively. The values of blood ethanol concentration as reported in this study indicate they are far too low to have any forensic significance.