The effect of chronic hypotension on sustained attention, short-term memory, arithmetic performance, and startle reflex modulation were investigated as they varied with circadian rhythms. Bodily temperature was also taken as a reference measure of circadian rhythm. Female university students, consisting of 17 hypotensives and 19 normotensives, participated in three sessions held in the morning, afternoon, and evening. Differences in attention were assessed using a reaction time task and prepulse modulation of the startle reflex. Short-term memory was evaluated using digit span and free recall of a word list. Arithmetic performance was measured using the Descending Subtraction Test. Bodily temperature was lower for the hypotensive subjects; however, temperature did not differ with circadian rhythm, and there were no significant circadian differences in the two groups. Furthermore, hypotensive subjects showed significant cognitive deficits compared with normotensives: reaction times were slower, memory was poorer, and arithmetic ability worse. Prepulse modulation of startle was also significantly different with the hypotensives showing larger reflexes than normotensives (lower attention allocation).