The peripheral blood levels of TNF alpha and its soluble receptors were studied in 39 patients with malignant and benign adrenal tumors treated by adrenalectomy. The concentrations of TNF alpha were significantly elevated in patients with malignant tumors of the adrenal cortex and in patients with Conn's syndrome compared to control. In patients with non-functioning adenomas and pheochromocytomas, TNF alpha levels were similar to those detected in the control. In subjects with myelolipomas, the serum concentration of TNF alpha was lower compared to the control. After adrenalectomy, the levels of TNF alpha were decreased in patients with malignant tumors and in patients with Conn's syndrome, non-functioniong adenomas and pheochromocytomas compared to the concentration before surgery. The serum concentrations of soluble receptors of TNF alpha did not differ among different patient groups and compared to the control. After adrenalectomy, the blood concentrations of TNF alpha R1 and TNF alpha R2 were decreased in patients with Conn's syndrome. However, to confirm practicality of the evaluation of TNF alpha and its soluble receptors in differential diagnosis in patients with adrenal tumors, a larger study group is needed.