In this work, a simple and fast method for the determination of diacetyl by gas-chromatographic technique coupled with flame ionisation detector (GLC-FID) was developed. Diacetyl is the typical butter flavour, but it is also commonly present in others fermented dairy products. Recently, diacetyl determination has also attracted interest because it is one of the parameters on which lactic acid bacteria (L.A.B.) are characterized and valued. Only acetone and 2,3-pentanedione were used as chemicals. After centrifugation of acetone-milk mixture, supernatant was filtered and directly injected into gas-chromatographic apparatus, without a further purification procedure step. This method was accurate and precise; diacetyl recovery on milk was 97% and the detection limit was 1 mg L-1. Finally, by using this method, diacetyl was easily determined in fresh and high-temperature treated milk, commercial butter, yoghurt and also in a series of L.A.B. performance tests. (C) 2007 Elsevier Ltd. All rights reserved.