The acute phase response involves changes in serum concentrations of a number of liver-synthesized proteins. Among these are C-reactive protein (CRP), ferritin (FER), transferrin (Trf) and ceruloplasmin (Cp). Determination of serum CRP, FER, Trf, and Cp was performed in 52 patients with inoperable head and neck cancer (n=11), inoperable esophageal cancer (n=10), rectal cancer (n=9; operation was performed=5, inoperable=4), and lung cancer (n=22), all of whom were treated with radical radiotherapy (RT). Post-radiotherapy CRP levels were significantly higher compared to the preradiotherapy levels (p<0.001). We found decreased serum Trf levels during the irradiation period, while acute-phase proteins such as CRP, FER, and Cp levels increased during the RT period. Further studies on the roles of other acute phase reactants and the above mentioned parameters in a large-patients-with cancer group during radiotherapy are required to understand the role of markers, which are altered during radiotherapy.