We investigated the activity and toxicity of raltitrexed (Tomudex) as a single agent treatment in patients with Malignant Pleural Mesothelioma (MPM) in a multicentre phase II European Organization for Research and Treatment of Cancer (EORTC) study. This study enrolled chemonaíve patients with histologically-confirmed measurable MPM. Raltitrexed was administered at the dose of 3 mg/m(2) intravenous (i.v.) bolus on an outpatient basis every 3 weeks. A maximum of eight cycles was planned in cases with an absence of progression or unacceptable toxicity. 24 patients received a total of 104 courses. 5 patients (20.8%, 95% confidence interval (CI) 7.1-42.2%) had a partial response (PR), which was confirmed by an independent radiology committee. Toxicity was mild, with diarrhoea, nausea, vomiting, fatigue and neutropenia as the major side-effects, but not exceeding grade 3 toxicity. We conclude that raltitrexed has activity as a single agent in the treatment of MPM, and that further studies with this drug in MPM are warranted.