[Truncated abstract] Cardiovascular reflex control of the vasculature is important in maintaining adequate tissue oxygenation in the face of disturbances in physiological homeostasis. Alterations in blood oxygen levels and blood distribution evoke integrated neural, mechanical and humoral responses which modulate peripheral vasomotor tone to maintain systemic cardiovascular integrity. The balance between the local effects of hypoxia and changes in chemoreflex control of vascular tone during hypoxia determine whether net vasoconstriction or vasodilatation is evident in the peripheral vasculature. The mechanisms contributing to hypoxic vasodilatation per se have not previously been defined in healthy humans. Study 1 of this thesis (Chapter 3) investigated the mechanisms contributing to vasomotor responses to chemoreflex activation in the human forearm ... Study 2 (Chapter 4a) investigated the mechanisms controlling vasomotor responses to isocapnic hypoxia in subjects with type 2 diabetes ... Study 3 (Chapter 5) compared the vascular responses to decreased venous return in individuals with and without right atrial afferent innervation ... The results of this thesis indicate that in healthy humans isocapnic hypoxia induces sympathetic vasoconstriction, which masks underlying β-adrenoceptor mediated vasodilatation. The normal vasomotor response to isocapnic hypoxia is impaired in subjects with type 2 diabetes. Despite intact vasoconstrictor responses, subjects with type 2 diabetes exhibited attenuated adrenaline-mediated vasodilatation compared to healthy control subjects, suggesting that the chemoreflex in these subjects is ill-equipped to respond to hypoxic stress. In clinical terms, impaired reflex vasomotor