We hypothesized that serial assessment of TGF-β1 during chemotherapy might predict therapeutic response and prognosis in non-small cell lung cancer (NSCLC) patients. Plasma TGF-β1 levels were quantified before first, second, and third cycles of chemotherapy in 42 advanced NSCLC patients and correlated with therapeutic response. Plasma TGF-β1 levels measured before first and second cycles of chemotherapy failed to predict response to therapy. The increased presence of TGF-β1 measured before second and third cycles of chemotherapy was associated with poor survival. Estimation of plasma TGF-β1 during the course of chemotherapy might not be a reliable biomarker for predicting therapeutic efficacy in NSCLC.