Plasma concentration of fibrinopeptide A (FpA) and D-dimer (DD), sensitive indicators of coagulation and fibrinolysis activation, were measured in 21 patients thyroidectomized for differentiated cancer (4 had distant metastases) and in 27 control subjects. Only two patients (one with distant metastases) presented elevated FpA values. All the four patients with distant metastases showed elevated DD levels. In three patients who developed distant metastases the time course of the circulating levels of plasma DD and serum thyroglobulin (Tg) was monitored. Monitoring of plasma DD concentration correctly indicated the time course of all the 3 metastatic patients while serum Tg levels failed to adequately describe the outcome of one metastatic patient. These data suggest that fibrinolysis is enhanced in thyroid cancer patients with distant metastases and that plasma DD levels are useful in the monitoring of this condition.