To determine the effect of the calcium blocker amlodipine on the variability of mean arterial pressure (MAP), amlodipine besylate was acutely administered to sino-aortic baroreceptor-denervated (SAD) rats (0, 1, 3, 10 mg/kg s.c.), and chronically administered to SAD and sham-denervated rats (0, 50, 150, 500, and 1,500 mg x kg(-1) feed, 4 days per dose). Acute amlodipine administration caused significant dose-dependent reductions of the mean MAP level and short-term MAP variability at the 3 and 10 mg/kg dose levels, respectively. Chronic administration produced dose-dependent reductions in short-term MAP variability, becoming significant at the 150 and 500 mg x kg(-1) feed dose level in SAD and Sham groups, respectively. Day-night differences in blood pressure were significantly attenuated or reversed at the 500 and 1,500 mg x kg(-1) feed dose levels. Amlodipine had little or no effect upon the 24 h MAP level, long-term MAP variability, and only modestly reduced the MAP response to hexamethonium. These results demonstrate that amlodipine can reduce MAP variability independent of changes in the mean blood pressure level.