This study was devised to determine whether blood loss for sequential bilateral knee arthroplasties was the same for the first and second knees. Twenty-eight patients who underwent this procedure were studied along with a control group of patients who underwent unilateral knee arthroplasties. Blood loss was greater in the second knee by a mean of 323 mL (P < .05). The control group and the first knee showed no significant difference in blood loss. Analysis of clotting studies showed a prolongation of prothrombin time, activated partial thromboplastin time, and thrombin time after release of the first tourniquet. Possible reasons for this greater blood loss are discussed.