The effects of four angiotensin-converting enzyme (ACE) inhibitors, captopril, enalapril, quinapril and alacepril, on the cough responses caused by citric acid and capsaicin inhalation were studied in normal and bronchitic guinea-pigs. After an oral dose of 10 mg kg-1, none of the ACE inhibitors had an effect on the citric acid-induced coughing response in normal guinea-pigs. Enalapril 10 mg kg-1 significantly increased the number of coughs caused by capsaicin inhalation. In bronchitic guinea-pigs, 10 mg kg-1 captopril and enalapril significantly increased the number of capsaicin-induced coughs. When administered daily for 8 days, captopril was the only ACE inhibitor which significantly increased the number of coughs due to citric acid inhalation. The present results indicate that the ACE inhibitors had different modes of cough augmentation.