The increased incidence of cancer of different kind [47], the presence of goiter and thyroid cancer [48,49] in acromegalic patients and certain experimental evidence of growth hormone (GH) signalling effects on thyroid growth [50], and also potential cancerogenic properties of insulin-like growth factor I (IGF-I) justify to evaluate effects of somatotrophic axis components on oxidative damage to macromolecules, also in the thyroid. Here, GH1 is linked to thyroid cancer.