Methodology is detailed that provides sustained concurrent measurement of fluid volume and electrolyte intake and output with direct measurement of arterial pressure in unrestrained, unanesthetized spontaneously hypertensive rats (SHR). This method employs an all-Teflon arterial pressure conduction system, an air-pressurized infusion system, and standard rat metabolism cages. Blood pressure-salt/water balance studies comparing SHR unoperated, sham operated, and infused at several infusion rates and saline normalities indicated that infusion of 0.25 N saline at 0.5 ml/h sustained a patent system for high-fidelity recording of systolic and diastolic blood pressure without distortion of homeostasis over a 3-week period. Studies of basal SHR blood pressure and salt/water balance suggested that the SHR primarily used renal water-conserving mechanisms to dilute net acquired salt over an 11-day period. This methodology for sustained blood pressure measurement appears to represent a significant improvement for direct blood pressure measurement in unrestrained, unanesthetized rats.