The aim of the study. Estimatation of p53 protein and soluble FasL ligand level concentration in serum of patients with benign and malignant primary follicular thyroid tumors as indicators of apoptosis and evaluation of their usefulness for early diagnosis of thyroid tumors.Material and methods. 42 patients were qualified for the study. 28 patients were diagnosed with follicular neoplasm (NF) in preoperative fine-needle biopsy. The final verification was postoperative histopathology. Control group consisted of 14 patients with euthyroid goiter, with no cancerous cells detected in cytologic examination. All patients underwent surgical procedures. Levels of p53 and sFasL were marked on the day of admission, before surgery. Destinationes were made in the serum using the ELISA immunoenzymatic method. Obtained data underwent computer statistical analysis.Results. The analysis revealed significantly higher sFasL and p53 concentration in blood of patients with follicular thyroid cancer in comparison with the control group. Similarly, p53 serum level was significantly higher in case of patients with benign thyroid adenoma than in the control group. Comparison between p53 and sFasL serum level in cases of patients with follicular cancer and follicular adenoma showed statistically higher sFasL blood concentration in cases of patients with follicular cancer; there was no statistically significant connection in case of p53 concentration.Conclusions. 1. sFasL and p53 serum concentration are significantly higher in patients with follicular thyroid cancer than in the control group. 2.The p53 serum concentration is significantly higher in cases of all patients with benign thyroid adenoma than in the control group. There was no such correlation for sFasL concentration. 3. sFasL serum concentration is significantly higher in cases of patients with follicular thyroid cancer than in patients with benign thyroid adenoma. There was no such correlation with serum levels of p53.