To study the characteristics of our outpatient clinic patients presenting with chronic cough as the sole symptom of bronchial asthma, and to evaluate the bronchial hyperreactivity of such patients in comparison with that of classic asthmatic patients with normal spirometry. For 3 years we studied 193 consecutive patients with chronic cough as the sole symptom, using the study protocol specified in the section on patients and methods. Sixty-three patients were diagnosed of bronchial asthma. Bronchial hyperreactivity was considered to be the cause of coughing based on reversibility testing or a positive methacholine test, along with response to specific antiasthmatic therapy. Forty-six (73%) of the 63 patients had unproductive cough and 28 (44%) coughed mainly at night. In 14 (22%) symptoms began with an upper respiratory tract infection. Wheezing could be heard in only 4 (6%). Diagnosis was based on reversibility in 11 (17%) and methacholine testing in 52 (83%). Mean PC20 was higher in patients diagnosed of variant cough. Unlike classic asthma, persistent and usually unproductive cough caused by asthma has few or no accompanying symptoms. The diagnostic yield of methacholine testing is high in such patients.