ObjectiveTo compare enalapril 20 mg once daily with 10 mg twice daily in terms of blood pressure reduction and patient compliance.DesignCross-over study of patients randomly assigned to a sequence of enalapril 20 mg once daily or 10 mg twice daily in three 4-week periods following a 4-week placebo run-in.SettingGeneral practices in the greater Belfast and Lisburn area in Northern Ireland.PatientsTwenty-five hypertensive patients who had a mean diastolic blood pressure of between 90 and 110 mmHg after receiving placebo for 4 weeks.Main outcome measuresReduction in blood pressure and estimation of patient compliance.ResultsPatient compliance was superior on the once daily regimen. However, the twice daily regimen was associated with a greater blood pressure reduction which almost reached statistical significance at the 5% level.ConclusionsEnalapril 20 mg should be prescribed as 10 mg twice daily and measures taken to improve patient compliance.