In several papers an increased quantity of cell-free plasma DNA as well as the presence of long DNA fragments in cell-free plasma and serum has been described. We isolated cell-free DNA from plasma, serum, and bronchial lavage supernatants from 33 lung cancer patients and 27 patients with a benign lung disease. The DNA was amplified by real-time PCR, and the quantity as well as the DNA integrity was determined. We did not find significant differences between the patient populations. Our results led us to conclude that this method is not useful in a diagnostic setting and is not able to differentiate between lung cancer patients and patients with a benign lung disease.