In the northeast part of Turkey where the goitre is endemic the copper content of the urine of 100 patients was examined by atomic absorption spectroscopy. The mean daily urinary copper levels were high at 18.4 +/- 4.29 mug in a goitrous population compared to a control population with 14.3 +/- 3.70 mug living in a non-endemic area (p < 0.01). Twenty-four hour urinary copper levels increased as the size of the gland increased: 16.0 +/-4.16 mug in grade I, 18.4 +/- 38 mug in grade II, 18.7 +/- 4.28 mug in III and 20.7 +/- 5.39 mug in grade IV. Twenty-four hour urinary copper content was statistically higher in grade IV patients compared to grade I patients (p < 0.001). The results suggest that copper may play a role in the etiology of endemic goitre, perhaps by augmenting the effects of iodine deficiency.