Abstract The phosphorylation of α-crystallin B was studied in homogenates of autopsy samples of brain tissue from patients with Alexander's disease, a condition characterized by over-expression of this protein. After incubation in the presence of [γ- 32P]ATP and cAMP the homogenates were analyzed by two-dimensional electrophoresis, (isoelectric focusing followed by SDS-PAGE). Three major polypeptides having the same molecular weight as bovine lens α-crystallin B and pIs 7.1, 6.9 and 6.7 were detected in the Coomassie blue stained gels. These three polypeptides were recognized by an α-crystallin B-specific antiserum in Western blots. The polypeptides with pIs 7.1 and 6.7 co-migrated in isoelectric focusing gels with bovine lens αB and its phosphorylated form αBp, respectively. Radioautography of the two-dimensional gels demonstrated the presence of 32P in the most acidic polypeptide. The results demonstrate the occurrence of αB phosphorylation in Alexander's disease brain tissue.