To initiate the inflammatory cascade leading to demyelination in multiple sclerosis (MS) T cells have to recognize their specific myelin antigen, which needs to be presented in the context of major histocompatibility (MHC) class II molecules expressed on antigen presenting cells. Whether astrocytes can express MHC class II molecules in vivo is a controversial issue. We performed double labeling immunohistochemistry in postmortem samples from nine patients with MS, three patients with a cerebral infarction and six controls. Astrocytes in controls, in normal appearing white matter in MS, and at the boundary of infarctions were MHC class II negative. In contrast, a subset of astrocytes in active chronic plaques immunostained for MHC class II, indicating potential antigen presenting interactions of astrocytes in MS.