The medullary thyroid carcinoma (MTC) occurs in the two major forms, the sporadic medullary carcinoma (SMTC) and hereditary medullary carcinoma, to which belong familial form (FMTC) and the element of Multiple Endocrine Neoplasia Syndrome MEN 2A and 2B. The method-of-choice of treatment is total thyroidectomy with following radiotherapy in selected cases. Among the follow-up methods, there are two used the most frequently: the pentagastrin and omeprazole stimulation test of calcitonin (CT), and CEA antigen assay. The aim of this study is to evaluate usefulness of plasma CT, CEA and AFP assay in the early detection of relapse or metastasis of MTC. 18 patients (14 females and 4 males) were investigated. The following procedures were performed in all the patients: plasma CT assays in the basal conditions and after stimulation tests, CEA and AFP. The results were analysed according to TNM staging and neck USG results. Our conclusion is that calcitonin stimulation tests, and CEA assays are useful methods to estimate the presence of relapse or metastases in the patients after surgical treatment due to MTC. Assays of plasma AFP concentration are not useful in a follow-up of patients operated on MTC.