methods PatientsTwenty-three patients (13 women aged 36-87 years, 10 men aged 41-81 years) with pheochromocytoma were recruited. Eighteen cases of benign pheochromocytoma and five cases of malignant form were diagnosed. The following were obtained from all patients: clinical history, basic laboratory tests and specialist biochemical tests (plasma metanephrine and normetanephrine levels, serum CgA concentration), abdominal imaging [computed tomography (CT) and/or magnetic resonance imaging (MRI)]. Also, in selected patients scintigraphy [ 123 I-metaiodobenzylguanidine scintigraphy ( 123 I-MIBG) and/or somatostatin receptor scintigraphy (SRS)] was also done. After pharmacological preparation, all patients were referred for surgical treatment (laparoscopic or classic surgery). The diagnosis of pheochromocytoma was confirmed by histopathological examination of tumour specimens and by immunohistochemical assays (CgA and synaptophysin). The control group consisted of 35 healthy volunteers (blood donors): 17 women aged 19-48 years and 18 men aged 20-52 years. In this group, plasma levels of metanephrine and normetanephrine as well as serum CgA levels were determined. In both groups of subjects (patients with pheochromocytoma and healthy participants) the plasma concentration of the proSAAS peptide was determined.