The pyrimidine antimetabolite gemcitabine is an analogue of cytosine arabinosid. Gemcitabine is well tolerated when given in doses of 1000-1250 mg/m2 weekly x 3 followed by 1 weeks rest, with mild myelosuppression as the major toxicity. In five studies, including a total of 250 patients with previously untreated non-small cell lung cancer (NSCLC), response rates from 20 to 28% were observed, ranking gemcitabine among the active agents in NSCLC. Gemcitabine should be further explored in combination therapy for NSCLC.