12 untreated subjects (ages 59–84 years; 9 male, 3 female) with isolated systolic hypertension participated in a single-blind dose-ranging study to assess the hypotensive effect and tolerability of felodipine. With dosing periods of 2 weeks’ duration, after a placebo run-in phase, felodipine was commenced at 2.5mg twice daily and increased to 5mg and then 10mg twice daily if predose systolic blood pressure was > 160mm Hg and diastolic blood pressure was > 70mm Hg. Nine subjects completed the study. At the highest attained felodipine dose, blood pressure 2 hours after the first dose was reduced by 25/12mm Hg supine and 26/17mm Hg standing compared with the placebo run-in phase. 12 hours after the last dose blood pressures were also lower than those in the placebo run-in phase but were similar to values after the placebo washout phase. The sequential design of this study has thus not allowed separation of treatment and period effects. Withdrawals were for vasodilator adverse effects, intercurrent illness and blood pressure below criteria for continuation. Four of the 9 patients completing the study also reported vasodilator side effects. It was concluded that a felodipine dose range of 2.5 to 10mg twice daily is appropriate for further studies in this patient group.