BACKGROUND: Imidapril is an angiotensin converting enzyme (ACE) inhibitor without a sulfhydril group which has been shown from previous study to have low incidence of ACE inhibitor induced cough. OBJECTIVE: To compare the incidence of cough between two ACE inhibitors, imidapril and enalapril. MATERIAL AND METHOD: A comparative cross over study was performed in 119 patients with hypertension or left ventricular dysfunction. Patients were assigned to one of the two treatment groups, either a group receiving imidapril or enalapril for 4 weeks (Period I) and then these same groups were crossed over to receive either enalapril or imidapril for 4 weeks (Period II). The occurrence of cough during treatment was monitored by interviewing the patients. RESULTS: The incidence of cough was 44 % while on imidapril treatment and 66% while on enalapril treatment (p = 0.0014). The antihypertensive effects of two drugs were not different. CONCLUSION: The incidence of cough was significantly less under imidapril than under enalapril treatment, while there was no difference in the antihypertensive effects between the two ACE inhibitors.