The aptitude of resting cells of Brevibacterium linens G171 to synthesize S-methyl thioesters was studied in presence of methanethiol and nine short-chain fatty acids individually or as a mixture. Esterification of acetic, propionic and methyl branched-chain acids occurred with methanethiol alone and was enhanced by fatty acid addition. Addition of n-chain, 3-hydroxybutyric and 2-hydroxyvaleric acids allowed synthesis of n-chain thioesters up to thiocaproate. The kinetics of production and the effect of concentrations of both substrates and of cells were tested. The optimum pH for synthesis varied according to the kind of thioesters produced. Results suggested that thioesters were derived mainly from acyl-CoA from different metabolic breakdowns, such as the degradation of fatty acids or some amino acids, and that several acyltransferases could be involved.