In order to investigate whether patients with euthyroid multinodular goitre (EMG) lose more iodine through urinary excretion than is to be expected due to an elevated renal clearance of iodine and/or whether the iodine is handled differently in the thyroid of these patients than in that of normal subjects, the following data were obtained for 33 patients with EMG and 30 normal subjects: thyroid clearance (TC), absolute iodine uptake (AIU), renal 123I clearance (RC) and plasma inorganic iodine (PII). A significantly lower PII and a higher TC was found in the goitre patients. In the control group PII appeared to be higher and TC and RC lower in the older age group (greater than 50 years). The difference in PII and TC is most easily explained by a higher iodine uptake in the subgroup of normal subjects over 50 years of age. AIU did not differ in any of the groups. Thus, it may be concluded that an endogenous iodine deficiency due to elevated renal clearance of 123I is not a factor in sporadic goitre, at least in our patients. At the observed plasma iodine levels a significantly higher AIU was not found for goitrous patients.