To assess the plasma TGF-β1 level during radio(chemo)therapy and to test the predictive power of TGF-β1 for treatment response in patients with advanced head and neck cancer. Twenty nine patients with advanced head and neck cancer were treated with curative radio(chemo)therapy. Plasma TGF-β1 level was established at the beginning, in the middle and at the end of the therapy. The dynamics of the TGF-β1 level was assessed separately for patients with and without chemotherapy. Treatment response was correlated to the TGF-β1 level. Eighteen patients achieved complete remission, eight partial remission and three patients progressed. Patients treated with radiotherapy had significantly higher initial plasma TGF-β1 level compared to radiochemotherapy patients (p=0.044). During the treatment, there was a significant decrease in patients treated with radiochemotherapy (p=0.008) but not in radiotherapy patients (p=0.34). Tumor burden did not correlate with plasma TGF-β1 level (p=0.07). TGF-β1 has no predictive value for treatment response (CR vs. PR and PD, p=0.12). The combination of radiotherapy and chemotherapy significantly decreases plasma TGF-β1 level in patients with advanced head and neck cancer. Treatment response cannot be predicted using TGF-β1.