By example of two cases a newly available tool, the recombinant humane thyroid stimulating hormone (rhTSH) is discussed in its use as an adjunct in diagnosing and treating differentiated thyroid carcinoma with radio-iodine. This product is an easier and safe alternative to the necessary rise of TSH induced by thyroid hormone withdrawal and concurrent hypothyroidism. Although discrepancies in favour of the classical approach have been demonstrated in some patients, the clinical relevancy of these must be weighted against the advantage of avoiding undesirable symptoms and possible tumour growth by the use of rhTSH. The role of rhTSH in the follow-up diagnosis and radioiodine treatment of thyroid carcinoma will undoubtedly increase in importance.