Forty-eight patients with freshly diagnosed carcinoma of the lung (40 males, 8 females) were evaluated for a coagulation profile including activated partial thromboplastin time (aPTT), prothrombin time (PT), fibrinogen, F VIII R:Ag, fibrin monomers (FM), thrombin-antithrombin-III complex (TAT-III), D-dimers and the platelet count. Thirty-eight patients had a normal aPTT and 37 patients a normal PT. None of the patients had clinical or laboratory indications of serious hemorrhage or thrombosis. On the other hand, high percentages of increased values were found for fibrinogen and F VIII R:Ag, which can be seen as prethrombotic factors. The very high percentages of elevated results for the FM, TAT-III and D-dimer are strongly indicative for low-grade coagulation activation with reactive fibrinolysis. Nevertheless, most lung cancer patients are able to maintain a normal or near normal hemostatic function. The results shown here are indicative of a coagulation and fibrinolysis equilibrium at an enhanced level and demonstrate why an unbalance between the two systems can result in thrombotic complications in (lung) cancer patients as earlier reported.