The -adrenergic pathway has been considered one important effector of circadian variation in arterial pressure. Experiments were performed in 1/2-adrenergic receptor-deficient mice (1/2ADR-/-) to assess whether this pathway is required for circadian variation in mean arterial pressure (MAP) and to determine the impact of its loss on the response to changes in dietary salt. Twenty-four hour recordings of MAP, heart rate (HR) and locomotor activity were made in conscious 16-17 week old mice (wild-type, WT, n = 7, 1/2ADR-/- n=10) by telemetry. Both WT and 1/2ADR-/- mice demonstrated robust circadian variation in MAP and HR, although 24 hour mean MAP was 10% lower (102.02 ± 1.81 vs. 92.11 ± 2.62 mm Hg) in 1/2 ADR-/- than WT, HR was 16% lower and day-night differences reduced. Both WT and 1/2ADR-/- adapted to changed salt intake without changed MAP. However, the 1/2ADR-/- mice demonstrated a striking reduction in locomotor activity in light and dark phases of the day. In WT, MAP was markedly affected by locomotor activity, resulting in bimodal distributions in both light and dark. When MAP was analyzed using only intervals without locomotor activity, bimodality and circadian differences were reduced, and there was no significant difference between the two genotypes. The results indicate that there is no direct effector role for the -adrenergic system in circadian variation of arterial pressure in mice, aside from for the indirect consequences of altered locomotor activity. Our results also confirm that locomotor activity contributes strongly to circadian variation in BP in mice.