The identification of anaerobic bacteria to the species level can be a laborious and time consuming procedure. Gas chromatography offers a diagnostic aid, and the advantages of the recently introduced head-space gas chromatography technique are: it is rapid, accurate and easy to perform; it provides more information of differential diagnostic value; and the identification process can be automated by connecting the head-space gas chromatograph to an automatic injection unit and a computer which interprets the chromatograms. The head-space technique may be used for direct analyses of clinical specimens for rapid diagnoses of anaerobic infections.