Blood pressure changes occurring over a 24-h period are under behavioral, humoral and reflex regulation. The sympathetic nervous system modulates blood pressure variation by affecting cardiac output and peripheral vascular resistance. This paper reviews evidence for the relationship between adrenergic neural drive and blood pressure as measured by direct and indirect approaches. This paper also reviews the sympathetic activity associated with increased 'in-office' and 'out-of-office' blood pressure, that is, the white-coat and the masked-hypertensive states. Finally, this paper examines altered neuroadrenergic influences on nocturnal blood pressure reduction and blood pressure variability.