Bronchial Reactivity. Its Measurement and Clinical Significance**

Summary: Bronchial reactivity was measured in 19 normal and 21 asthmatic subjects as the percentage fall in FEV1,0 after a graded dose of inhaled methacholine. The mean fall was 6 per cent in normal and 44 per cent in asthmatic subjects. It is suggested that a simple and specific test for asthma, based on this response, has a definite place in the routine pulmonary function laboratory. This test can be clinically useful in establishing or excluding the presence of bronchial asthma in cases where the diagnosis may be otherwise uncertain.