In this review, we deal with six groups of cytotoxic drugs commonly used in the treatment of non-small cell lung cancer (NSCLC). Although there are many reviews of thymidylate synthase (TS) and antifolate inhibitors, in this article, we have tried to highlight aspects that are more important for medical oncologists to consider when treating NSCLC patients. There is compelling evidence that TS gene transcripts and TS polymorphisms could be used to decide which patients can best benefit from adjuvant chemotherapy approaches, especially in colorectal cancer, and not less importantly, to tailor chemotherapy in metastatic NSCLC when using drugs akin to fluorouracil, such as pemetrexed. Secondly, cisplatin is central to chemotherapy combinations and evidence indicates that DNA repair capacity influences response to cisplatin-based regimens. ERCC1 gene transcript stands out as a predictive marker of cisplatin sensitivity. Thirdly, preliminary studies indicate that upregulation of beta-tubulin III correlates with response to paclitaxel and vinorelbine. Fourthly, overexpression of ribonucleotide reductase can influence response to gemcitabine. Fifthly, we describe mechanisms of resistance to topoisomerase I inhibitors, although this subject has not yet been completely elucidated. Finally, to understand the mechanisms of resistance to EGF-R inhibitors, which have been shown to be useful in many different types of cancer, the Src-STAT signaling pathways are described here in detail. Hopefully, the assessment of Src and of STAT-3 can be implemented as predictive markers.