In a single-center open label study we evaluated the effects of magnesium sulphate (MgS) infusion on the sublingual microcirculation perfusion in fluid resuscitated patients with severe sepsis and septic shock within the first 48 hours after ICU admission. Directly prior to and after 1 hour of magnesium sulphate (MgS) infusion (2 gram) systemic hemodynamic variables, sublingual SDF images and standard laboratory tests, were obtained.