The validity of various scintigraphic and endocrinological methods was assessed in order to classify confirmed autonomous adenomas (AA) and to differentiate AA from euthyroid and hyperthyroid goitres. Methods used included: Measurement of 131J-uptake 6, 24 and 48 hours after 131J-application, before and after suppression by T3, thyroid scanning, count-rate measurement in the AA and the paranodular tissue, and determination of T4. All patients received 131J-therapy (40,000 rads). In 8 out of 30 scintigraphically compensated autonomous adenomas (CAA) there was no TSH response to TRH. 12 cases showed a subnormal TSH response and 10 patients had a normal TSH response. T4-values were increased in only 2 cases. Out of 73 decompensated autonomous adenomas (DAA), 66 cases (90%) had no TSH response and 7 cases showed only a subnormal response. In 48% of DAA T4-levels turned out to be in the hyperthyroid range. Both, scintigraphic and endocrinological tests were found to agree in most cases of DAA. However, the diagnosis of CAA could only be proved on the basis of a scintigraphically confirmed suppressive effect of T3 on the paranodular tissue. Thus, in the individual case, separation of CAA from DAA turned out to be impossible using the results of TRH-test alone.