Thyroid carcinomas are the most frequently occurring tumours in the endocrine system. Metallothioneins (MT) and Ki-67 proteins are present in intensely proliferating cells, and their expression has been observed in numerous tumours, including thyroid tumours. The purpose of this study was to analyse the relationship between intensity of MT expression and Ki-67 antigen on one hand and histological features of the examined thyroid tumours on the other. The investigated material included 186 archival paraffin blocks with samples of various thyroid tissues, obtained from the Chair and Department of Pathomorphology, Medical University of Wroclaw. In paraffin sections, immunohistochemical reactions were performed with the use of monoclonal anti-MT (I/II) and anti-Ki-67 antibodies. Intensity of MT and Ki-67 antigen expression was evaluated using a light microscope using the semi-quantitative method of Remmele. A significant difference in MT expression was noted between different tumours of the thyroid: the highest expression was detected in follicular carcinoma and the lowest was detected in medullary carcinoma. Expression of MT was also significantly elevated in follicular carcinoma as compared to follicular adenoma. On the other hand, no significant differences were seen between expression of Ki-67 antigen in follicular adenoma and follicular carcinoma. Moreover, these investigations detected no correlation between the expression of MT and Ki-67 antigen in follicular adenoma and follicular carcinoma. In view of the obtained results, the expression of MT can be considered as a potential marker of differentiation between the two types of thyroid tumours, which are otherwise difficult to differentiate.