The study presents data comparing the new tumor marker Tumor M2-PK with CEA, CYFRA 21-1, NSE and SCC in the diagnosis of lung cancer. Tumor M2-PK is quantitatively detectable in EDTA-plasma with a sensitive ELISA. The results of the tumor marker test were compared with respect to the different histological tumor types and with the tumor staging. So far 144 newly diagnosed lung cancer patients were included. Significantly elevated tumor marker concentrations were found with progressive tumor stages. The best correlation with the tumor stage was observed for Tumor M2-PK and CYFRA 21-1. Comparison of the sensitivities in the detection of lung cancer indicated that the Tumor M2-PK-test (sensitivity: 58%) is more efficient than the CEA-Test (sensitivity: 39%) or CYFRA 21-1 (sensitivity: 48%). Generally higher sensitivity for non-small cell lung cancer only was shown for Tumor M2-PK (sensitivity: 65%), CEA (sensitivity: 42%) and CYFRA 21-1 (sensitivity: 58%). For small-cell lung cancer the marker NSE was more sensitive than all other markers. Initial follow-up studies indicate that Tumor M2-PK and CYFRA 21-1 can be used to monitor disease with tumor progression or regression during chemotherapy. The present data indicated that Tumor M2-PK could be a valuable tumor marker for the detection of lung cancer.