Preweanling physical and behavioral development was studied in spontaneously hypertensive (SHR), borderline hypertensive (BHR), and Wistar-Kyoto normotensive (WKY) rat pups. Measures of physical development included body weight, onset of various morphological landmarks, and speed of surface righting. Behavioral tests assessed locomotor development, exploratory behavior, and cliff avoidance in pups of the 3 groups. On all measures employed, SHR pups exhibited a delay in physical maturation compared to age-matched BHR and WKY pups. Results from the locomotor development test revealed that young WKY pups (ages 1-7 days) spent more time locomoting than SHR pups, with BHR times being intermediate. In contrast, older SHR pups (ages 17-30 days) displayed greater activity in an exploratory maze than WKY pups, with BHR values again intermediate. Finally, SHR pups were more behaviorally reactive in the cliff avoidance task compared to BHR and WKY pups. These group differences may be useful in understanding the development of genetic hypertension and may serve as early behavioral markers of a predisposition to cardiovascular disease.