The immunoglobulin (IgG, IgM, IgA) content of normal, reactive and migrated rat astrocytes was studied in lesioned adult rat cortex and after fetal cortex grafts. Implantation pockets were aspirated in the somatomotor cortex (under bregma) of adult Sprague-Dawley rats. A fetal (E14) rat hemicortex incubated in the plant lectin Phaseolus vulgaris leucoagglutinin (graft premarker) was placed in the aspiration pocket or the pocket left empty (control). Sections of brain were immunohistochemically double labeled for immunoglobulins-GFAP or Phaseolus vulgaris leucoagglutinin-GFAP 3-60 days postoperative. Mature or fetal astrocytes in situ did not contain immunoglobulins. In pocket-only animals, individual reactive astrocytes lining and subjacent to the pocket were positive for rat IgG, IgM and IgA (3-60 days). In grafted animals, graft derived astrocytes (Phaseolus vulgaris leucoagglutinin-GFAP positive) were intermingled with host reactive astrocytes (Phaseolus vulgaris leucoagglutinin negative) lining and subjacent to the pocket. Both classes of astrocytes contained immunoglobulins IgG, IgM and IgA. Immunoglobulin positive graft derived astrocytes migrated into the corpus callosum, cingulum and habenula. These results demonstrate that astrocytes sequester immunoglobulins and probably other serum proteins as a critical function in restoring homeostasis to the injured or diseased nervous system.