Background: Systemic absorption of iodinated contrast material occurs during endoscopic retrograde cholangiopancreatography (ERCP), the clinical significance of which has not yet been determined. Methods: Urinary iodine excretion was measured before and after coronary angiography (n = 20) and ERCP (n = 12). Thyroid hormone levels were determined before iodine load and after 6 and 24 weeks. Results: Before coronary angiography, iodine excretion was 101 ± 38.3 μmol/mol creatinine and increased to 865 · 10⁵ ± 721 · 10⁵ μmol/mol on the next day (p ≤ 0.001). After 6 weeks, it was still elevated (167 ± 88.8 μmol/mol, p < 0.01). Before ERCP, iodine excretion was 115 ± 60.3 μmol/mol and reached a peak of 5.3 · 10⁵ ± 4.9 · 10⁵ μmol/mol (p < 0.001). Six weeks later, it had returned to baseline. Two patients in the coronary angiography group but none in the ERCP group had suppressed thyrotropin after 6 weeks. Conclusions: The systemic iodine load during ERCP is approximately 0.6% of the iodine load during coronary angiography. Therefore routine measurement of thyroid hormones before ERCP is not recommended. (Gastrointest Endosc 1999;50:79-81.)