BACKGROUND: Small cell lung cancer (SCLC) frequently presents as metastatic disease. It would be useful to detect serum tumor biomarkers at an earlier stage in order to improve the overall survival. MATERIALS AND METHODS: Serum samples from SCLC patients (6 limited disease, 7 extensive disease, 4 relapsed disease, 4 no evidence of disease post-treatment) and 5 normal controls were used to identify tumor biomarkers utilizing proteomics. Serum hepatocyte growth factor was also studied using standard ELISA. RESULTS: Utilizing MALDI-TOF-Mass Spectrometry (MS) based protein identification techniques, a SCLC specific overexpressed protein was identified to be haptoglobin alpha-subunit, with its serum level correlating with the disease stage. The mean level of alpha-haptoglobin was increased in SCLC serum as compared to the normal controls. Serum HGF was also studied as potential tumor biomarker and was found to correlate with the disease status. Either serum alpha-haptoglobin relative level (above 1.9 U), or HGF level (above 500 pg/ml) was associated with a trend towards worse survival. CONCLUSION: Our current findings suggest that serum levels of alpha-haptoglobin and HGF may serve as useful serum tumor biomarkers in SCLC. It would now also be useful to determine if these serum biomarkers are altered in response to therapy for this disease.