['Little is known about the whole body oxidative stress burden following radioactive iodine ((131)I) therapy of thyroid diseases.', "We studied 17 patients with benign nodular goiter treated with (131)I therapy. The targeted thyroid dose was 50 Gy in 11 patients pretreated with 0.1 mg of recombinant human TSH (rhTSH). In 6 patients, the applied thyroid dose was 100 Gy without rhTSH prestimulation. Well-established biomarkers of oxidative stress to RNA (8-oxo-7,8-dihydroguanosine; 8-oxoGuo) and DNA (8-oxo-7,8-dihydro-2'-deoxyguanosine; 8-oxodG) were measured in freshly voided morning urine (normalized against the creatinine concentration) at baseline, and 7 and 21 days after rhTSH (not followed by (131)I), and 7 and 21 days after (131)I therapy, respectively.", 'The baseline urinary excretions of 8-oxoGuo and 8-oxodG were 2.20 ± 0.84 and 1.63 ± 0.70 nmol/mmol creatinine, respectively. We found no significant changes in the excretion of any of the metabolites, neither after rhTSH stimulation alone nor after (131)I therapy. Also, no significant differences were found between the rhTSH group (low dose, median (131)I: 152 MBq) and the non-rhTSH group (high dose, median (131)I: 419 MBq; 8-oxoGuo: p = 0.66, 8-oxodG: p = 0.71).'] Is systemic oxidative stress to nucleic acids unaltered following radioiodine therapy of patients with benign nodular goiter?