The concentration of carbohydrate-deficient transferrin in serum (CDT) has been used as a reliable indicator of recent alcohol consumption. We have investigated the utility of this laboratory test in 20 patients with hereditary haemochromatosis (HH) by simultaneous evaluation of serum concentrations of liver transaminases, gamma-glutamyl transpeptidase, iron, transferrin and assessment of the liver iron concentration by magnetic resonance imaging. 11 patients were re-examined during iron depletion with phlebotomies. In all 11 patients intensive but not maintenance iron removal was associated with an increase in serum CDT, in three patients even to levels above the reference range. The mean serum CDT increased from 8.5 (SD 2.2) U/l to 16.6 (SD 7.2) U/l (P < 0.001). Iron mobilization from the liver was found particularly responsible for the increase in serum CDT. Independent of this finding we found a significant semi-logarithmic correlation (r = -0.77, P = 0.009) between the MRI determined liver iron concentration and serum CDT in the patients not on iron depletion. Our findings indicate that the utility of serum CDT as a measure of alcohol consumption in patients with HH may be compromised, especially during intensive iron depletion.