Abstract: Exposure of Saccharomyces cerevisiae to 0.9 mM sorbic acid at pH 4.5 resulted in the upregulation of 10 proteins; Hsp42, Atp2, Hsp26, Ssa1 or Ssa2, Ssb1 or Ssb2, Ssc1, Ssa4, Ach1, Zwf1 and Tdh1; and the downregulation of three proteins; Ade16, Adh3 and Eno2. In parallel, of 6144 ORFs, 94 (1.53%) showed greater than a 1.4-fold increase in transcript level after exposure to sorbic acid and five of these were increased greater than two-fold; MFA1, AGA2, HSP26, SIP18 and YDR533C. Similarly, of 6144 ORFs, 72 (1.17%) showed greater than a 1.4-fold decrease in transcript level and only one of these, PCK1, was decreased greater than two-fold Functional categories of genes that were induced by sorbic acid stress included cell stress (particularly oxidative stress), transposon function, mating response and energy generation. We found that proteomic analysis yielded distinct information from transcript analysis. Only the upregulation of Hsp26 was detected by both methods. Subsequently, we demonstrated that a deletion mutant of Hsp26 was sensitive to sorbic acid. Thus, the induction of Hsp26, which occurs during adaptation to sorbic acid, confers resistance to the inhibitory effects of this compound. Copyright 2001 John Wiley & Sons, Ltd.