OBJECTIVES: It has been argued that monoclonal antibody 17-1A (MAB) is more effective in colon cancer (CC) than in colorectal cancer (CRC) Dukes´ C. The purpose of this analysis was to estimate the cost effectiveness of MAB in CC versus observation only from the perspective of a third-party payer in Germany. METHODS: The investigation was based on a sub-group analysis of original data from patients with CC within the clinical trial in patients with CRC. The modelling approach used the cost-effectiveness ratios `additional cost for MAB per life-year gained (LYG)´ and `per disease-free-year gained (DFYG)´. LYG and DFYG after 5 years were obtained from the corresponding Kaplan-Meier curves. Relapse prevention with MAB was nearly twice as effective in CC than in CRC. Economic consequences of resource use, collected from a survey, were determined by multiplying utilised items by the prices or tariff of each item. Costs and effectiveness were discounted by 5% per year. RESULTS: The base-case analysis revealed additional cost for MAB of 5,380 DM per LYG and 4,860 DM per DFYG, when a scenario of 30% inpatient and 70% outpatient administration was applied. In the sensitivity analysis, there were net savings of 3,820 DM per LYG and 3,450 per DFYG in the case of exclusive inpatient administration up to additional cost for MAB of 9,320 DM per LYG and 8,420 DM per DFYG, when MAB was administered on an outpatient basis exclusively. CONCLUSIONS: MAB is very cost effective in patients with CC. In inpatient administration, it results in net savings for the third-party payer while improving patients' prognosis at the same time.