Alcohols, ketones and aldehydes have been identified in the profiles of volatile substances in blood serum. A 5-ml sample is required in order to obtain a complete gas chromatographic profile, selective profiles of alcohols or individual ketones by computer mass fragmentography, and to permit mass spectrometric identification of the compounds. The quantitative determination of total 4-heptanone using an extraction and gas chromatographic-mass fragmentographic procedure demonstrated concentrations of 10-50 nmole/l in normal serum, whereas in the serum of patients with chronic renal insufficiency the concentrations were 10- to 40-fold higher. Ethanol and total acetone were quantitatively measured by direct injection of serum. For 10 patients, concentrations between 25 and 85 mumole/l of acetone and 10-170 mumole/l of ethanol were determined.