The immunoreactive protein for the tissue inhibitor of the metalloproteinase (TIMP)-1 and -2 as well as for the matrix metalloproteinase (MMP)-2 and -9 was quantified from the sera/plasma of 90 lung cancer patients and 20 control subjects with enzyme linked immunoassays (ELISA) using specific monoclonal antibodies. Free MMP-2 and that bound to the inhibitor, the MMP-2/TIMP-2 complex were measured separately using different ELISAs. For the detection of MMP-9, TIMP-1 and TIMP-2, the total protein was measured to quantify both free and complex forms. Serum protein levels for TIMP-1, TIMP-2 and the MMP-2/TIMP-2 complex differed significantly in patients with lung cancer when compared to controls. TIMP-1 levels were found to be higher in lung cancer than in controls, whereas TIMP-2 and MMP-2/TIMP-2 complex levels were lower in lung cancer than in the sera of the control subjects. High TIMP-1 (> 300 ng/ml) or MMP-9 (> 30 ng/ml) correlated to poor cumulative survival in lung cancer patients (log rank P < 0.05). High TIMP-1 indicated a poor prognosis, especially in squamous cell cancer and in NSCLC patients with stage III: 66% and 70%, respectively, of the patients with low TIMP-l serum levels survived for more than one year, when only 25% and 20%, respectively, of the patients with high serum levels for TIMP-1 protein survived at that time. 56% of lung cancer patients with a plasma MMP-9 level < 30 ng/ml survived for 12 months when only 31% of the lung cancer patients with high MMP-9 plasma levels survived for more than one year. Also this difference was significant (log rank analysis, P < 0.05). Our results suggest that the factors of the metalloproteinase system might be important in lung cancer progression. TIMP-1 as well as MMP-9 could serve as prognostic markers, and their values could be investigated in the follow-up of lung cancer patients when selecting patients for systemic chemotherapy or other treatment modalities.