Traditional cytotoxic anticancer therapies do not differentiate between tumour and host cells, and research efforts have been focused on finding new agents that target tumour tissue. Gefitinib (‘Iressa’, ZD1839) is an orally active epidermal growth factor receptor tyrosine kinase inhibitor that blocks signal pathways implicated in solid tumour growth and metastasis. In phase II trials, gefitinib 250 mg/day demonstrated efficacy in the control of advanced non-small-cell lung cancer (NSCLC) in patients who had undergone prior chemotherapy. Response rates were 18·4 and 11·8%, and disease control rates were 54·4 and 42·2%, at 250 mg/day in two multicentre trials – IDEAL 1 and 2. Gefitinib also caused rapid relief from the symptoms of NSCLC in approximately 40% of patients, while displaying a generally good tolerability profile that most commonly included mild, reversible gastrointestinal and skin adverse events. Gefitinib 250 mg/day has been approved for use in advanced, previously treated NSCLC in several countries including the USA, Japan and Australia. As a monotherapy and combination therapy, it is being investigated for the treatment of several common tumour types in addition to NSCLC. The pharmacokinetics of gefitinib have shown it to be suitable for once daily dosing, with a terminal half-life of approximately 48 h in patients with cancer. Steady-state exposure is achieved after 10 days dosing, and exposure is dose proportional up to 250 mg/day. Gefitinib is cleared principally by the biliary route and in part by metabolism. This review summarizes relevant data from studies of gefitinib that inform its clinical administration.