In advanced cases of non-small cell lung cancer, cytostatic treatment has small but assessable effect on patient survival as opposed to only symptomatic therapy. Cytostatic drugs, however, are known to have numerous side effects including neurotoxicity, nephrotoxicity, and myelosuppression. Better knowledge of tumor biology has led to the discovery of several key molecular pathways. Due to their beneficial effect and side effect profile, epidermal growth factor receptor tyrosine kinase inhibitors (gefitinib, erlotinib) have now been included in clinical practice in the treatment of non-small cell lung cancer. The predictive characteristics for the indication of these drugs have not yet been cleared up and require further clinical studies. Under the Expanded Access Program it has become possible to give patients with advanced non-small cell lung cancer (stages III/B and IV) epidermal growth factor receptor tyrosine kinase inhibitor erlotinib. Authors present here two cases to illustrate the beneficial effect of the drug when used as second or third line therapy. A more detailed study of the histological specimen (epidermal growth factor receptor expression as well as epidermal growth factor receptor gene mutation) will provide further information as to the anticipated efficacy for erlotinib.