Changes in the concentrations of antioxidant (Cu, Zn superoxide dismutase catalase, ceruloplasmin, and transferrin) and recently discovered pro-oxidant (cytochrome B-558 I-IV and suprol, a superoxide producing lipoprotein) metalloproteins and cytochrome B-5 were assessed in the blood of anesthesized and control rats. The concentrations of antioxidant and pro-oxidant metalloproteins varied. They were not changed during anesthesia, except suprol. As for the qualitative changes, phospholipid composition was altered, superoxide production decreased, and lipid peroxidation of suprol increased during anesthesia. The authors propose using antioxidant metalloproteins for decrease of the undesirable consequences of halothane anesthesia in experimental medicine.