This is a prospective study that will be conducted over a one year period of time. Eligible patients will be identified by a search of patients who are receiving vancomycin therapy throughout the study period. Chart review/patient interview will then be performed to identify patients who developed symptomatology consistent with RMS while receiving vancomycin infusion. For the purposes of this study, red man syndrome (RMS) will be defined as: erythematous rash, flushing of the face, neck, or torso, itching, or a lowering of systolic or diastolic blood pressure by >10mm/hg. A subset of patients who remained asymptomatic throughout their vancomycin therapy will also be evaluated as a control group.