The purpose was to investigate the effect of neutralization of rat interleukin-6 (IL-6) bioactivity on the activity levels of Na+ -K+/Mg++ adenosine-5'-triphosphatase and superoxide dismutase, and the degree of infarct size in ischemic brain produced by experimental middle cerebral artery occlusion in the rat. Seventy adult male Wistar rats weighing 280 to 310g were used in this study. The animals were randomly allocated to Groups: group I (n = 10) consisted of normal controls, group II (sham-operated, n = 20) underwent surgical exposure of the middle cerebral artery but 110 cauterization, and the remaining 40 rats were subjected to middle cerebral artery occlusion. Immediately after occlusion. each of these 40 rats was randomly assigned to either the occlusion-only group (group III, it = 20) or the occlusion plus IL-6 antibody treatment group (group IV, n = 20). All evaluations were performed in blinded fashion. Our data provide evidence that neutralization of IL-6 bioactivity correlates with less secondary damage in long-term treatment after focal cerebral ischemia in the rat.