Hyperthyroidism induced by contrast agents in a major problem in patients with pre-existing thyroid disease, particularly in patients with functional thyroid autonomy. The present study was undertaken to evaluate whether contrast media applied during endoscopic retrograde cholangiopancreaticography (ERCP) may result in a significant increase of serum iodine levels and thus may be associated with the risk of iodine-induced hyperthyroidism. The courses of serum concentrations of total iodine and free iodide, as well as of urinary iodine excretion, were measured in 15 patients before and up to 21 days after ERCP. During ERCP, the non-ionic contrast medium iopamidol was instilled in amounts resulting in a total iodine load of 57.4 +/- 22.8 mmol (7.3 +/- 2.9 g). In all patients, ERCP resulted in a highly significant increase in serum levels of total iodine from 0.8 +/- 0.5 to 85.2 +/- 116.9 mumol/l 4 h after application of the contrast agent. In parallel, serum iodide levels were raised from 0.06 +/- 0.04 to 5.42 +/- 6.09 mumol/l and urinary iodine excretion from 71.1 +/- 35.7 mumol/mol creatinine to 621,620.9 +/- 636,492.2 mumol/mol creatinine. Peak concentrations of serum iodine are well related to the total amount of iodine applied (p < 0.05). During follow-up, iodine levels returned to pre-exposure levels within 2-3 weeks. Levels of thyrotropin, free thyroxine, and free triiodothyronine remained unchanged during the follow-up period. In conclusion, endoscopic application of iodinated contrast agents during ERCP leads to significant increases of serum levels of total iodine and free iodide and of urinary iodine excretion.(ABSTRACT TRUNCATED AT 250 WORDS)