Thyroid imaging was performed using technetium-99m methoxyisobutylisonitrile and technetium-99m pertechnetate in 58 patients. The 99mTc-pertechnetate scans showed a total of 77 nodules: 60 cold, 13 hot and 4 of normal activity. There was no 99mTc-MIBI accumulation in 46.4% of 99mTc-pertechnetate cold nodules; 27 (45%) of these nodules showed 99mTc-MIBI uptake with the same intensity as the surrounding normal tissue, and five (8.6%) became hot with 99mTc-MIBI. Of the 99mTc-pertechnetate hot nodules 11 (84.6%) could not be differentiated from the normal extranodular tissue on the 99mTc-MIBI scan. The histopathology of 34 surgically removed nodules proved that increased, normal or decreased 99mTc-MIBI accumulation is not specific for thyroid malignancy and that the 99mTc-MIBI uptake depends mainly on the viability of thyroid tissue.