Reaction time (RT) was compared in 160 hypertensive and 43 normotensive adults. After being screened for coronary and cerebrovascular disorders, each subject completed 12 variations of a serial RT task. Subjects were blocked into normotensive, nonmedicated hypertensive, and medicated hypertensive groups, and into three age groups: 18-31; 32-45; 46-59. Response slowing was observed with increasing age. Significant slowing was also seen in the medicated but not the nonmedicated hypertensive group. Plasma renin activity (PRA) interacted with the medication factor; longest RTs were obtained for treated subjects with low and normal PRA and untreated subjects with high PRA. These results were interpreted in terms of changes in ability to autoregulate cerebral blood flow as a result of vascular damage.