This is a prospective randomized clinical study to determine if prophylactic antibiotics affect intra-operative culture results in patients undergoing revision hip or knee arthroplasty surgery for infection. Pre-operatively, patients will have their affected joint aspirated and this fluid will be sent for cultures. Patients are then randomized to receive prophylactic antibiotics (Vancomycin and Ancef) within one hour prior to surgery or to have pre-operative antibiotics withheld. Every patient then has their affected joint cultured intra-operatively. All samples will be evaluated for the presence of aerobic bacteria, anaerobic bacteria, mycobacteria, and fungus. Pre-operative and post-operative cultures in both study populations are compared to determine the effects of pre-operative antibiotics.