To compare the degree of clinical manifestations and bronchial obstruction in acute asthma, we correlated lung function tests with the clinical symptoms in 33 patients during acute attacks of bronchospasm induced by specific and non-specific inhalation challenge tests and compared the results with similar challenge tests in 12 healthy subjects. It could be shown that about 60% of the patients did not reveal wheezing or dyspnoea despite marked bronchial obstruction, thus indicating a poor sensitivity of clinical symptoms in relation to the objective alterations in the lung function tests. We therefore conclude that the degree of bronchospasm may be seriously underestimated if it is related only to the subjective complaints and the physical sign of expiratory wheezing. In particular, during inhalative bronchial challenge tests the asthmatic airway reaction should be carefully monitored by serial or continuous lung function tests in order to avoid major complications.