This paper reviews the toxicity profile of gemcitabine in a large group of patients (up to 790) from pivotal phase II studies, in which the drug was given intravenously as a 30 min infusion, in a schedule once a week for 3 weeks followed by a week of rest. The safety profile of gemcitabine is unusually mild for such an active agent in solid tumours. Haematological toxicity is mild and short-lived with modest WHO grades 3 and 4 for haemoglobin (6.4% and 0.9% of patients), leukocytes (8.1% and 0.5%), neutrophils (18.7% and 5.7%) and platelets (6.4% and 0.9%). The incidence of grade 3 and 4 infection associated with this level of myelosuppression was low (0.9% and 0.2%). Transaminase elevations occurred frequently, but they were usually mild, and rarely dose limiting. Mild proteinuria and haematuria were seen but were rarely clinically significant. There was no evidence of cumulative hepatic or renal toxicity. Nausea and vomiting was mild, rarely dose limiting, and generally well controlled with standard antiemetics. Flu-like symptoms were experienced in a small proportion of patients but were of short duration. Where oedema/peripheral oedema was experienced there was no evidence of any association with cardiac, hepatic or renal failure. Hair loss was rare, with WHO grade 3 alopecia reported in 0.5% of patients. There was no grade 4 alopecia. Furthermore, gemcitabine displayed minimal toxicity in elderly patients, and the side-effect profile does not seem to be affected by patient age. The adverse events typically experienced with cytotoxic agents, namely myelosuppression, nausea and vomiting and alopecia, are not seen to such a degree with gemcitabine, and this nonoverlapping toxicity profile suggests that gemcitabine is a promising agent for incorporation into combination chemotherapy regimens.