In a double-blind, parallel-group multicentre study in general practice, lisinopril (10-20 mg once daily) was compared with metoprolol (100-200 mg once daily) in 360 patients whose diastolic blood pressure (DBP) was in the range 91-115 mmHg despite diuretic treatment. Following a three week run-in period during which the diuretic was withdrawn, monotherapy with either lisinopril or metoprolol was given for two months with dose doubled after one month if DBP remained greater than 90 mmHg. Quality of life was assessed using established and validated questionnaires at the time of cessation of diuretic treatment and again after two months's active treatment. Both metoprolol and lisinopril achieved statistically significant BP reduction relative to baseline (P less than 0.001). Significantly fewer adverse events were experienced on lisinopril and metoprolol than on diuretic treatment. Frequency of withdrawals due to adverse events were statistically significantly lower on lisinopril than metoprolol P = 0.01. Before treatment approximately 35% of the patients had quality of life problems measured by General Health Questionnaire (GHQ), which was reduced to 17% on lisinopril and 23% on metoprolol. Thus both metoprolol and lisinopril were effective and safe in the treatment of mild to moderate essential hypertension with lisinopril being better tolerated. From patients' self-assessments of quality of life, lisinopril was found to be superior to metoprolol in some aspects of emotional, cognitive and social functioning.