This paper reviews the toxicity profile of gemcitabine, a novel anticancer drug. Gemcitabine has been administered using two different treatment schedules: once weekly or twice weekly for 3 weeks followed by a week of rest (one cycle). It was well tolerated and alopecia was not a problem. Toxicity was greater in the twice-weekly schedule. Comparing the once-weekly with the twice-weekly schedule, WHO grade 3 or 4 thrombocytopenia was reported in 4.7 and 25.6% of patients, respectively. Other hematological toxicity was minimal. Transient WHO grade 3 or 4 elevations of ALT and AST occurred in 9.2 and 7.2% of patients, respectively, in the once-weekly schedule. For the twice-weekly schedule the corresponding percentages were 12.2 and 13.8%. Symptomatic toxicity was greater in patients who received twice-weekly gemcitabine. Nausea and vomiting was mild and generally well controlled without 5HT3 antagonists. However, there was a greater incidence of nausea and vomiting on the twice-weekly schedule. Flu-like symptoms were documented in 19.8% of patients receiving once-weekly and 63.3% of patients receiving twice-weekly gemcitabine. Peripheral edema, not related to cardiac, hepatic or renal failure, was seen more often in patients on twice-weekly treatment. As the efficacy of gemcitabine in non-small cell lung cancer was equivalent when using both regimens, the better tolerated and more easily administered once-weekly schedule is recommended.