In an open field spontaneously hypertensive rats (SHR) exhibited lower scores for grooming when compared to their normotensive controls, the Wistar-Kyoto rats (WKY). After i.c.v. injection of 1 microgram ACTH cumulative 50-min grooming scores were lower in SHR. Analysis of subscores indicated that the lesser effect of ACTH in SHR was especially prominent for headwashing and anogenital grooming. Moreover, a time course study revealed that the difference between SHR and WKY occurred in the first 6 observation periods of 5 min and thereafter disappeared. The results are discussed in the light of behavioral and central neurochemical differences between SHR and WKY.