Bronchial asthma is the most frequent chronic disease in childhood. Nevertheless, no definition of the disease is known that would enable a satisfactory epidemiological recording of asthma. In 704 schoolchildren, typical signs and symptoms of asthma were recorded within the framework of a standardized interview. The occurrence of asthmatic symptoms was quantified by means of a symptom score. In 555 of the probands, bronchial reactivity was tested by means of an inhalative challenge with carbachol. The information gathered from the interview and the carbachol challenge test was placed in relationship to the family doctor's diagnosis of "bronchial asthma". Lifetime prevalence of asthma diagnosed by the family doctors is 4.97% with a clear male predominance. The asthmatic symptoms showed varying frequencies and validity compared with the family doctor's diagnosis. The occurrence of dyspnoea appears to be particularly sensitive (77%). Dyspnoea coincident with exercise is highly specific (99%). The sensitivity of the combination of carbachol test and symptom score is 92% and the specificity is 75%. The instruments described above offer a reliable possibility for epidemiological field research to record the prevalence of bronchial asthma in schoolchildren.