Eighty-eight patients referred consecutively for thyroid imaging were studied. Each patient was scanned with a 3'' rectilinear scanner using both 125I and 99mTc. The paired scans were evaluated independently by two physicians experienced in thyroid evaluation and image analysis. The images were ranked on a scale from 1 to 5 as follows: 1) 125I scan much better than the 99mTc scan, 2) ..., 3) 125I scan and 99mTc scan the same, 4) ..., 5) 99mTc scan much better than 125I scan. The scores were statistically analyzed by the sign test and transformed normal score methods. Categories analyzed were: A. Hypothyroid, B. Euthyroid, C. Hyperthroid, (A-C based upon RAIU measurements), D. Cold Nodules, E. Graves Disease, F. Hot-Nodules, G. Multinodular Nontoxic Goiter, H. Miscellaneous and I. Normal. The significance of this study is that regardless of the classification we used, in no category was the 99mTc scan considered better than the 125I scan. This finding is at variance with the observations of some others comparing 99mTc with other iodine radioisotopes. 99mTc may have some procedural advantages and does deliver a lower radidation dose to the thyroid.