Cytotoxic chemotherapy treatment options for patients with non-small-cell lung cancer (NSCLC) have limited efficacy and are often associated with significant toxicity. Therefore, there is an unmet need for novel drugs that are not only effective in treating this disease but are also well tolerated. Gefitinib is an orally active epidermal growth factor receptor tyrosine kinase inhibitor that blocks the signal transduction pathways implicated in cancer cell growth and survival. It has recently been approved for the treatment of advanced/refractory NSCLC. This review presents the tolerability data from phase I and II gefitinib monotherapy trials, along with data from the worldwide 'Expanded Access Programme' and post-marketing use of gefitinib. Gefitinib was found to be generally well tolerated at the approved dosage of 250 mg/day; the most commonly reported adverse drug reactions (ADRs) were mild to moderate skin rash and diarrhoea, which were manageable and non-cumulative. Other ADRs observed with the use of gefitinib included: dry skin, pruritus, acne, nausea, vomiting, anorexia, asthenia and asymptomatic elevations in liver transaminase levels. Well recognised adverse effects seen with cytotoxic chemotherapy (such as bone marrow depression, neurotoxicity and nephrotoxicity) were not observed. Although the frequency and severity of ADRs increased with the dosage across the range studied (50-1000 mg/day), few patients required dosage reductions or the withdrawal of treatment, and those who did usually received gefitinib >or=600 mg/day.Thus, the available data indicate that gefitinib is well tolerated in patients with a range of solid tumours, including locally advanced or metastatic NSCLC.