Thioredoxin reductase is a member of the pyridine nucleotide-disulfide oxidoreductase family of enzymes. By delivering reducing equivalents to thioredoxin, thioredoxin reductase exerts control over a number of redox-sensitive factors in the cell, including ribonucleotide reductase and several transcription factors. We have localized the human thioredoxin gene to chromosomal position 12q23-q24.1 by in situ hybridization. We have also determined the relative tissue distribution of thioredoxin reductase mRNA as well as thioredoxin mRNA by probing a Northern blot of several human normal tissues.