The endogenous aliphatic alcohols ethanol, n-propanol, n-butanol, isobutanol and isopentanol in serum and urine were measured by gas chromatography-mass fragmentography. Whereas for the higher-molecular-weight alcohols extraction with dichloromethane is used, ethanol is determined by direct injection of serum and urine. When zero is assigned to all values below the detection limits of the procedures (0.1 mg/l for ethanol and 2 micrograms/l for each of the higher-molecular-weight alcohols) the following normal ranges are found: ethanol, 0-39 mg/l in serum and 0-46 mg per 24 h in urine; n-propanol, 0-48 micrograms/l in serum and 0-300 micrograms per 24 h in urine; n-butanol, 0-20 micrograms/l in serum and 0-18 micrograms per 24 h in urine. The isobutanol and isopentanol levels in the serum and urine of normal subjects are below the detection limit. For diabetic patients, on average increased levels are found for ethanol, n-propanol and n-butanol in serum and urine.