TNF, a cytokine produced by macrophages, is able either to exert an antitumor activity, or to determine severe clinical complications, such as cachexia and septic shock. Increased blood levels of TNF have been described in cancer patients. The present study was performed to better define TNF secretion in patients with solid tumors. The study included 48 cancer patients (lung cancer: 22; colon cancer: 11; breast cancer: 10; renal cancer: 5), and among them 27 showed distant organ metastases. TNF serum levels were measured by IRMA method. The control group comprised 40 healthy subjects. TNF levels were also evaluated in relation to those of SIL-2R, whose increase seems to be associated with an unfavorable prognosis in cancer. High levels of TNF were seen in 27/48 (56%) patients. Mean levels of TNF were significantly higher in cancer patients than in controls. Moreover, within the cancer group, TNF mean values were significantly higher in metastatic patients than in those without metastases; the highest levels were observed in patients with visceral lesions as dominant metastasis sites. Finally, patients with high TNF concentrations showed significantly higher mean levels of SIL-2R than those with normal values. This study shows that the neoplastic metastatic disease is associated with an exaggerated TNF secretion.