Although some evidence exists to support the use of clinical factors such as performance status and weight loss to predict response and toxicity to therapy in non-small cell lung cancer (NSCLC) patients, researchers have shown little prospective data on the use of molecular markers to facilitate selection of specific chemotherapy or new molecularly targeted agents in this patient population. Breast cancer exemplifies the growing role that molecular markers are playing, not only as prognostic factors, but also in predicting response to targeted treatments such as hormonal therapy, and more recently, trastuzumab (Herceptin). Although several studies have examinedmolecular markers in lung cancer and have shown promising potential value, these studies were retrospective and require prospective validation. To identify molecular markers that reliably predict response and to be able to individualize cytotoxic and targeted therapy for NSCLC patients are the ultimate goals of future trials. This article focuses on a selected number of promising markers under study in lung cancer, including those thought to play roles in response to DNA damaging chemotherapy (excision repair cross-complementing [ERCC1], xeroderma pigmentosum group D [XPD]), taxane resistance (-tubulin III), antimetabolite therapy (RRM1), irinotecan metabolism (UGT1A1) and epidermal growth factor receptor (EGFR) pathway inhibition. To date, none of these markers can be recommended for routine use in clinical practice.