Urine samples for the measurement of urinary excretion of droxidopa and metabolites including but not limited to 3-OM-DOPS, NE, vanillic acid, and protocatechuic acid will be collected before and over the following intervals after dosing: 0 2, 2-4, 4-6, 6-8, 8-12, 12-24, and 24-36 hours for healthy volunteers and subjects with mild, moderate, and severe renal impairment.