Volatile metabolites produced during Kluyveromyces lactis fermentation were identified and their kinetics examined. More than 50 compounds identified in the fel mentation broth were mainly benzenoid hydrocarbons, alcohols, carboxylic acids, esters, carbonyl and heterocyclic compounds. Predominant components were isoamyl alcohol, isobutanol, 2-phenylethanol, isobutyric acid, isovaleric acid, 2-phenylethyl acetate, 2-phenylethyl isobutyrate and 3-hydroxy-2-butanone. The level of total volatile metabolites increased almost in parallel with biomass during fermentation. The major individual components showed kinetic patterns. Accumulation of carboxylic acids appeared to induce a change in secondary metabolism at a late stage of fermentation.