The author studied the characteristics of ACE inhibitor-induced cough in 41 non-smoking hypertensive patients. For at least 6 months, 20 patients (10 males and 10 females) were treated with enalapril, and 21 (11 males and 10 females) with aracepril. The results were as follows. 1) ACE inhibitor-induced cough was induced in 7 cases (1 male and 6 females). The incident rate of cough was 17.1%. ACE inhibitor-induced cough was not significantly related to past allergic history or to the beta-adrenergic blocker therapy. The laboratory findings of the cough sufferers--such as eosinophil percent in venous blood, serum GOT and GPT, urea nitrogen, creatinine, renal function (PSP excretion test and creatinine clearance), and pulmonary function (%FVC, FEV1.0% and %V25)--were not significantly different from those of the non-coughers. 2) Inhibitory effects of ipratropium bromide inhalation of ACE inhibitor-induced cough were noted in 83.3% of the patients, but their coughs did not completely disappear. From these findings, the pathogenesis of this cough may be related to be as follows. The cough seems to be related to the release of acetylcholine from vagal nerve terminals or to the stimulation of irritant receptors and vagal reflex. 3) Chronic persistent cough or bronchial asthma did not occur after stopping the treatment with ACE inhibitors. The mean follow-up period was 15.6 months.