Our objective was to establish the balance between costs and effects of treatment with Tomudex (raltitrexed) as an alternative to treatment with B-fluorouracil (5-FU) plus leucovorin (LV) in patients with advanced colorectal cancer. Data were used from an international, open label randomized clinical trial. Costs were calculated by multiplying resource utilization data with Dutch estimates of unit costs. Effects have been expressed in terms of 6 months and 1 year survival, and in terms of the number of patients without severe adverse events including WHO grade 3 and 4 leucopenia, mucositis, anemia and severe asthenia. Cost effectiveness is expressed in terms of costs per additional day of survival and costs per additional patient without any severe adverse event. The clinical results did not show significant survival differences implying great uncertainty about the cost-effectiveness of raltitrexed in terms of additional costs per additional life-year gained. However, 80% of the initially higher cost of raltitrexed ($3132 per patient) is compensated by savings due to a more convenient administration scheme leading to a net cost of $626 per patient treated. Weighed against the decrease in adverse events, a cost-effectiveness ratio results of $3936 per additional patient free of any severe adverse event, More favorable estimates result when the convenience of the administration scheme is valued in positive monetary terms, [(C) 1999 Lippincott Williams & Wilkins.]