The efficacy of sustained-release verapamil as a first-stage treatment for mild to moderate, uncomplicated essential hypertension was studied. Nineteen patients aged 36-70 years (mean +/- SD 55 +/- 10 years) entered the study. Treatment with 240 mg sustained-release verapamil, once daily for 8 weeks, caused systolic and diastolic blood pressures to decline significantly during the first 2 weeks and this lower level was maintained until week 8. Heart rate decreased gradually during the treatment period reaching significance at week 8. After 2 weeks maximum systolic and diastolic blood pressures during isometric exercise were significantly reduced compared with pre-treatment values; there was no difference in the percentage increase occurring pre- and post-treatment. These measures for heart rate did not change significantly. Except for a significant reduction in cardiac index after 8 weeks left ventricular function and left ventricular mass were unchanged. The 24-h urinary Na+ excretion increased significantly after 2 and 8 weeks' treatment. Plasma renin activity, serum lipid concentrations and routine blood chemistries were not affected. Side-effects were transient and did not require discontinuation of therapy. In conclusion, sustained-release verapamil is an efficacious and well tolerated first-stage drug in the treatment of essential hypertension.