The efficacy and safety of enalapril and its effects on the quality of life were evaluated in 1017 Puerto Rican patients with uncomplicated mild to moderate essential hypertension. Enalapril was administered for 4 weeks in an open label, noncomparative study. Initially, patients received enalapril 5 mg and the dosage was titrated upwards, according to response, to a maximum of 20 mg/day. The goal of therapy was to achieve a diastolic blood pressure (DBP) less than 90 mm Hg. The study included 468 male and 545 female patients (mean age 52.6 +/- 11.9 years). A subgroup of 294 elderly patients was also evaluated (mean age 65.9 +/- 6.1 years). Mean blood pressure decreased from 157/99 mm Hg to 138/84 mm Hg (p less than 0.0001) in 966 patients who received enalapril as monotherapy. Mean blood pressure decreased from 164/99 mm Hg to 143/85 mm Hg (p less than 0.0001) in the elderly patients. After 4 weeks of enalapril monotherapy, 67% of the patients had a DBP less than 90 mm Hg. Enalapril was very well tolerated. Headache and dizziness were the most frequently reported side effects. Among the patients who completed a quality of life questionnaire, more than 70% reported feeling the same or better and less than 2% reported feeling worse after enalapril therapy. In conclusion, enalapril seems to be an excellent alternative as initial therapy in young and elderly Puerto Rican hypertensive patients.