The epidemiologic surveillance framework that has provided the basis for most of the studies of asthma epidemics in Barcelona was reviewed. The various steps from the identification of the epidemics to the establishment of their cause were considered. From 1981 to 1986, 12 outbreaks of asthma were identified in Barcelona. During these outbreaks, clinicians noted an extraordinary and hourly clustered influx of asthma patients. Analyses of air pollution indices, meteorological conditions, and geographic distribution of the cases revealed a simultaneous time and space clustering suggestive of a point source epidemic occurring in the harbor area. Studies of subsequent asthma outbreaks in 1987 suggested a possible relationship with the unloading of soybeans in Barcelona harbor. Immunologic studies provided evidence that an airborne soybean particulate antigen, reactive with serum from epidemic asthma patients, reached the city on epidemic days. This research in Barcelona, using principles of epidemiologic surveillance, has resulted in the identification of a specific etiologic hypothesis that has been tested using analytic designs. The validity of this hypothesis has been demonstrated and has enabled the causative point source to be removed. After this was done, no other asthma outbreaks were observed. The limitations and possibilities of the use of asthma emergency admissions data for research were discussed.