results We identified the TthIII I polymorphism as a C to T mutation, 3807 bp upstream from the mRNA start site. We found 39·7% CC-carriers, 44·5% CT-carriers, and 15·8 % TT-carriers. No differences were found between TthIII I genotypes in sensitivity to DEX, baseline cortisol, insulin, glucose or cholesterol levels, or in anthropometric variables. However, all ER22/23EK-carriers also carried the TthIII I T-allele, and carriers of both these polymorphisms had a significantly smaller cortisol suppression after 1 mg DEX, lower fasting insulin levels, and lower total and low-density lipoprotein (LDL) cholesterol levels than TthIII I T carriers without the ER22/23EK variant and noncarriers. No interaction was found between the TthIII I variant and N363S or Bcl I polymorphisms.