Fabry disease is a systematic genetic disease in which patients have abnormal blood vessels, and leads to numerous complications including cerebrovascular strokes. The objective of this study is to test the hypothesis that patients with Fabry disease have abnormal endothelial-derived vasodilation. If found to be abnormal, endothelial-derived vasodilation will serve as a useful clinical outcome measure in the evaluation of the efficacy of specific treatment of Fabry disease, and possibly of other causes of cerebrovascular stroke. The endothelium modulates vascular tone by the release of contracting and relaxing substances that act on the underlying smooth muscle. It has been previously demonstrated that patients with essential hypertension have a blunted vascular response to acetylcholine (an endothelium-dependent vasodilator). In the present study, we shall analyze the regional vascular responses to acetylcholine and sodium nitroprusside alone, and in the presence of L-NMMA (an inhibitor of the synthesis of EDRF by endothelial cells) in 12 patients with Fabry disease and 12 normal age matched control subjects. We will infuse drugs into the brachial artery and will measure the responses of the forearm vasculature by means of strain gauge plethysmography. Forearm blood flow and vascular resistance at baseline and after infusion of vasoactive drugs, in Fabry patients, will be compared to the responses obtained in the healthy control population. This study will be performed with collaboration of Dr. Julio A. Panza, Senior Clinical Investigator from the Cardiology Branch, NHLBI.