Pranidipine (OPC-13340), a new dihydropyridine calcium antagonist, was given to 9 elderly hypertensive inpatients aged 64-79 years. Once-daily administration of pranidipine (1-2 mg) for 1-2 weeks decreased the 24-h average BP significantly from 167/92 mmHg to 150/83 mmHg without any change in pulse rate (PR) or the variabilities of BP and PR. The reduction of BP was observed exclusively during daytime (171/95 mmHg to 153/86 mmHg, p < 0.01 for SBP, p < 0.05 for DBP), while BP reduction during nighttime was significant only for DBP (157/84 mmHg to 146/79 mmHg, p > 0.05 for SBP, p < 0.05 for DBP). The analysis of the circadian rhythm by the cosinor method revealed that the acrophases of BP and PR were not changed significantly by the treatment with pranidipine. No adverse effects such as flushing and headache developed during the treatment. These results suggest that once-daily treatment with pranidipine is safe and exerts a sufficient antihypertensive effect during daytime with mild reduction of nighttime BP in elderly hypertensives. Furthermore, it does not alter the circadian patterns or variabilities of BP and PR. Thus, pranidipine may be useful as a monotherapy for elderly hypertensives.