Electron capture gas-liquid chromatography, when used to analyze derivatized extracts of spent culture media and body fluids under specified conditions, holds promise as a tool for use by physicians, hospitals, and clinical laboratories in identifying certain diseases and disease-producing organisms. The detection of certain disease processes and the identification of disease-producing organisms are based on qualitative or large quantitative differences in EC-GLC profiles or a combination of both. Various practical procedures are given for extracting and derivatizing compounds, such as carboxylic acids, hydroxy acids, alcohols, amines, and nitrosamines. The characteristics of the parameters essential for successful analysis are discussed. Species and, in some cases, strains have been differentiated by comparing EC-GLC profiles. Metabolic products are affected by change in substrate. Media that can be reproduced from lot to lot are essential in some studies. The volatile components detected by EC-GLC in spent culture media consist mostly of bacterial metabolites, but the volatile compounds detected in body fluids may be bacterial metabolites, volatile components produced by the host in response to an infection, metabolites of cells associated with host defense, or a combination of two or more of these groups of compounds. The EC-GLC profiles obtained by analysis of synovial and cerebrospinal fluids appear to have good potential for use in diagnosing certain forms of arthritis and meningitis. Well-documented samples are essential to establishing EC-GLC profiles representative of a particular disease. A moderately priced computer would greatly aid in data processing and could be especially useful in compensating for minor changes in the retention times of peaks, which can occur as a result of column aging or when columns are renewed. An approach to the identification of components detected by EC-GLC, which makes use of electron capture gas chromatography-mass spectrometry, is presented.