Fifty asthmatic children were tested for cholinergic bronchial sensitivity and subjected to a free running exercise test; 92% of them showed hypersensitivity to acetylcholine challenge, and exercise-induced bronchospasm occurred in 80%. On pooling the results, 98% had a positive response to at least one of the tests. Qualitatively, there was a correlation between exercise-induced bronchospasm and bronchial sensitivity to acetylcholin in 38 of the 50 children. Quantitatively, however, no correlation could be found between the severity of the exercise-induced bronchospasm and the threshold dose of acetylcholin. This could be explained by the fact that the non-immunological spasmogenic mechanisms involved in the two tests are different.