Analysis of the genome of the human pathogen, Aspergillus fumigatus, revealed the presence of several putative glutathione transferase (GST) open reading frames. Three A. fumigatus GST genes, termed gstA, B, and C, were cloned and recombinant proteins expressed in Escherichia coli. Functional analysis of recombinant gstA–C conWrms that the enzymes exhibit GST activity and glutathione peroxidase activity. RT-PCR conWrmed low basal expression of gstA and gstC which was markedly up-regulated (at least 4£– 10£) in the presence of either H2O2 or 1-chloro-2,4-dinitrobenzene (CDNB). GstB expression was only observed in the presence of CDNB. These results demonstrate for the Wrst time the existence of three functional GSTs in A. fumigatus and strongly suggest a role for these enzymes in the response of the organism to both oxidative stress and xenobiotic presence.