The ability of thioredoxin (Trx) to protect cells from chemical damage was determined by comparing the growth of a control strain of Escherichia coli JM101 and isogenic strain transformed with the plasmid pKKTS1 containing the Streptomyces aureofaciens thioredoxin gene, in the presence of the nucleoside analogs arabinosylcytosine, 5-fluorouridine, ftorafur and carcinogen beta-naftylamine. Arabinosylcytosine showed no effect on the growth of either of the two strains. 5-fluorouridine, ftorafur [1-((R,S)-tetrahydrofuran-2-yl)-5-fluorouracil] and beta-naftylamine demonstrated lower inhibitory effects on the growth of the thioredoxin overproducing strain than on the growth of the control strain. These results suggested that Trx could protect the cells from chemical damage under certain metabolic conditions.