A new system for monitoring cases of CO poisoning, implemented via a circular, has been piloted in the Pays-de-la-Loire and Aquitaine regions since January 2004. This system relies on a mechanism for reporting poisoning cases at the DDASS level. Following a report, environmental and medical investigations are conducted to characterize the cases and identify the source of the poisoning. The objectives of the study are to evaluate the functional qualities and performance of the system as well as the tools developed, in order to make recommendations regarding the expansion of the system to the national level as of January 1, 2005. The method used is based on the CDC and WHO surveillance system evaluation models. Quantitative indicators were constructed using data collected by the system. A survey was conducted among the departments that receive reports and conduct investigations (Ddass: 10 health-environment departments and 10 Misp, 10 SCHS) and the two Drass responsible for monitoring the system’s implementation. This survey was supplemented by a summary meeting with the various partners. As this evaluation took place after only a few months of operation, it provides information on only part of the system. The large number of people likely to be involved in combating carbon monoxide poisoning at the regional level complicates operations: regional working groups do not appear to be the operational level for the system’s deployment. The large number of identified reporters may pose problems regarding the dispersion of resources for mobilizing these various stakeholders. The system appears acceptable despite the workload involved in all the investigations, particularly home visits; however, the issue of understaffing is frequently highlighted. The system is responsive in terms of alerts and field investigations: the vast majority of alerts are issued the same day or the next day, and half of the cases are subject to a site visit within one day of the alert date. Overall, the forms are easy to use and acceptable in terms of the time required and technical skills needed, with the exception of the form for the environmental investigation: concerns were raised regarding the limited technical skills required, the risks involved during investigations, and the liability of the agents. The computer application was evaluated as simple and functional. A few recommendations can be made: among other things, give regions more latitude in organizing the surveillance system (prioritize departmental meetings, establish specific working subgroups), and organize technical training to standardize agents’ skills. (R.A.)