This report represents an attempt to combine the serum levels of more tumor markers together to evaluate the response to chemotherapy in 26 patients affected with small cell lung cancer (SCLC), by means of discriminant analysis. A pilot prospective study was performed on 26 subjects affected with inoperable SCLC (18 extensive diseases, and 8 limited diseases) and treated with chemotherapy (etoposide plus cisplatin regimen). Serum levels of a panel of tumor markers: Carcinoembryonic antigen (CEA), Tissue Polypeptide Antigen (TPA), Neuron Specific Enolase (NSE) and CYFRA -21.1 were determined before starting chemotherapy and at the restaging time (after 3 months). To optimize the classification power of these markers, a discriminant analysis was done, which permitted generating two classification functions, based on Tissue Polypeptide Antigen and Neuron Specific Enolase levels able to correctly classify 25 out of 26 subjects (8 progressions and 18 non progressions). The results obtained, furtherly confirm that tumor markers are useful to evaluate the chemotherapy response and indicate a possible approach to obtain the maximum usefulness of the serum marker levels.