Of the new chemotherapeutic substances of the last decade, gemcitabine (Gemzar, Eli Lilly) is probably the most valuable for the treatment of early and advanced stage non-small cell lung cancer (NSCLC). When used as a single agent in both chemotherapeutically pretreated and chemotherapy-naive patients, gemcitabine shows an objective tumor regression rate of approximately 20%. Gemcitabine's unique mechanism of action and its lack of overlapping toxicity with other cytotoxic agents also define it as an ideal candidate for combination therapy. Early clinical development has included single-agent first- and second-line treatment, doublet combination regimens and incorporation into multimodality treatment strategies for operable and inoperable locally advanced nonmetastatic NSCLC. Gemcitabine/platinum-based combination chemotherapy has become the most attractive treatment standard for NSCLC patients in good clinical condition. The role of gemcitabine in the concurrent or sequential application of chemo- and radiotherapy for inoperable locally advanced NSCLC has also been addressed in several Phase I and II studies. Based on data available, gemcitabine can be safely administered in combination with radiotherapy. This review summarizes results from representative Phase I, II and III studies in order to underline gemcitabine's clinical importance for patients suffering from early and advanced NSCLC.