Sera of 100 consecutive DTC patients after total thyroidectomy were to be collected at the Department of Nuclear Medicine both under TSH-suppression therapy and under endogenous TSH stimulation (TSH > 25 mU/l). All patients were staged by clinical examination, cervical ultrasound (7.5 MHz), I-131 whole-body scintigraphy and – where applicable – F18-FDG-PET. Written informed consent was obtained from all pts. Sera were taken in separation tubes without anticoagulants and stored at -20°C until analysis. Sera were allowed to come to room temperature prior to analysis.