Brain area 5-hydroxytrhptamine (5-HT) turnover and behavioral correlates were compared in spontaneously hypertensive rats (SHR) and normotensive Wistar rats. SHR appeared to have hyperfunctional 5-HT systems as evidenced by the finding that brain area 5-HT turnover times were 53% lower in SHR, with significant changes seen in the limbic forebrain. SHR, while less active upon initial testing of spontaneous motor activity than Wistar rats, did not habituate as readily to the testing procedures as evidenced by higher activity than Wistar rats in repeated testing stiuations. In the light of other data indicating that 5-ht systems are predominantly inhibitory to ongoing behavior, these data suggest that habituation, as determined in this study, is an active process that is retarded in the SHR because of hyperfunctional 5-HT systems. Spontaneous activity of SHR was inhibited less than that of Wistar rats by a conditioned stimulus which is consistent with the observations of others that 5-HT systems tend to suppress responsiveness to external stimuli. While spontaneous activity data suggested that SHR were more emothinal than Wistar rats, the SHR also exhibited a higher avoidance rate in an unsignaled shuttle avoidance procedure which is usually indicative of a lower emotional state.