Eighteen patients bearing a hot nodule, imaged by basal 99Tcm scintiscan and toxic in eight of them, were studied. All patients underwent 99Tcm thyroid scintiscan in basal conditions and after placing a lead-shield on the hot thyroid nodule, without other radioisotope administration. In eight cases the thyroid scintiscan after lead-shield overlapping the hot nodule, was compared to a second 99Tcm thyroid scintiscan after thyrotrophic hormone stimulation, TSH. This technique of nodule shielding was able to show the extranodular tissue in 15 patients; in the remaining three cases neither this approach nor the scintiscan after exogenous TSH were able to demonstrate any remainder thyroid parenchyma. Thus, this scintigraphic method can be considered excellent in the diagnosis of autonomous adenoma: it needs, in fact, a single radioisotope administration and does not present the adverse effects frequently induced by exogenous TSH.