The specific aim of this study is to determine whether water ingestion potentiates the pressor response to pseudoephedrine in patients with primary disorders of autonomic failure. The study design will enable us to also evaluate the pressor response to water alone and to pseudoephedrine alone. In a secondary analysis, we will compare the results in patients with two autonomic disorders, pure autonomic failure (PAF) and multiple system atrophy (MSA). We hypothesize that drinking water following a dose of pseudoephedrine will lead to a greater increase in blood pressure than pseudoephedrine alone.