Eighty one patients with uncomplicated hypertension who required additional antihypertensive medication (diastolic Phase V [dBP] greater than or equal to 95 mm Hg) after 4 weeks treatment with hydrochlorothiazide (HCTZ) 25 mg o.m. were randomized to receive felodipine 5 mg b.i.d. (n = 40) or propranolol (n = 41) 80 mg b.i.d. in addition to HCTZ 25 mg o.m. If the dBP measured about 12 h post-dose was not less than or equal to 90 mm Hg after 4 weeks, the dose of felodipine or propranolol was doubled. The double blind trial period was 8 weeks for all patients. Over the 8 week period, felodipine reduced the seated dBP from 100 to 83 mm Hg and propranolol from 101 to 86 mm Hg. The attained seated dBPs were significantly different in the two groups. About one third of patients in each group received the high dose of second-line therapy. After 8 weeks 91% of patients receiving HCTZ+felodipine and 84% receiving HCTZ+propranolol had a dBP less than or equal to 90 mm Hg. Both regimens were well-tolerated with an equal incidence but different pattern of adverse events (felodipine: flushing, headache and peripheral oedema; propranolol: dyspepsia, fatigue and vasospasm). In this 8-week study, felodipine and propranolol were safe and effective second-line antihypertensive drugs when added to hydrochlorothiazide. At the doses selected, felodipine was at least as effective as propranolol.