Angiotensin-converting enzymes, ACE and ACE2, play not only a pivotal role in the regulation of blood pressure, but are involved in the processes of pathophysiology, including thyroid dysfunction or progression of several neoplasia such as cancers of skin, lungs, pancreas and leukemia. However, their role in the thyroid carcinogenesis remains unknown. We examined in this study the expression of ACE and ACE2 in thyroid tissues and their possible employment as biomarkers for thyroid cancer progression. Thyroid tissues, including 14 goiters (G), 12 follicular adenomas (FA), 10 follicular thyroid carcinomas (FTC), 14 papillary thyroid carcinomas (PTC) and 11 undifferentiated thyroid carcinomas (UTC), were subjected to RT-PCR and protein analyses with primers or antibodies specific for ACE and ACE2, respectively. FA revealed significantly increased ACE compared to other groups and FTC was significantly higher than UTC. ACE2 was significantly increased in PTC in comparison to G, FA and UTC, and in FTC as compared to G. The ratio ACE/ACE2 decreased, while ACE2/ACE increased with the differentiation grade of thyroid carcinoma. ACE was significantly diminished in individuals older than 50. Both ACEs were significantly diminished in M1 patients, ACE2 additionally in higher tumor masses. ACE and ACE2 are regulated within thyroid benign and malignant tissues. As the transcript ratio between both enzymes correlate proportional with the differentiation status of thyroid cancer, ACE and ACE2 may serve as new markers for thyroid carcinoma.