If surveillance data is to be correctly interpreted, the degree of exhaustiveness and representativeness of the surveillance system must be known. The capture-recapture method, which can be used for this evaluation - provided that at least two data sources are available - was applied to the surveillance of meningococcal infections in France. To identify those cases common to both surveillance systems, cases of the disease occurring in 1989 and 1990 and appearing on detailed Mandatory Notification (MN) records (702 cases) or reported to the National Reference Centre (NRC) (727 cases) were compared. The total number of cases of meningococcal infection was estimated at 1,367, using the capture-recapture method. Exhaustiveness rates, which did not differ for the various bacterial strains, were 51% for MN and 53% for NRC, although large regional differences were found for both systems. More cases were notified to MN in the age group 5-24 (60%), than in other age groups (49%). Quarterly exhaustiveness rates were unrelated to incidence of the disease. A district by district analysis of the correlation between exhaustiveness rates for each system suggests that the two data sources were probably independent. Scrupulous identification of common cases and study of the independence of the two systems are indispensable prerequisites for using this method, which provides a good alternative to exhaustive studies.