Calbindin has been isolated and characterized as a calcium carrier protein in the gut enterocyte. This protein is also determined as a marker protein in the neuronal cell in hippocampal formation and the cerebral cortex (Baimbridge K.G. et al.: Trends Neurosci. 15; 303-308 (1992)). However, we also detected calbindin in the reactive astrocyte after ischemic delayed neuronal death. In order to make sure of this observation, another experimental lesion model, referred to as an electrical heat lesion, was employed. To prove the colocalization of calbindin and glial fibrial acidic protein (GFAP) as a marker protein of astrocyte, an immuno-fluoro double-stain method by conforcal fluoromicroscopy was carried out. Monoclonal mouse antibody for calbindin 28k was purchased from Boehringer-Mannheim and polyclonal antibody for GFAP was purchased from Dako Japan. Second antibodies for GFAP and calbindin antibodies were labeled by FITC and rhodamine, respectively. Conventional immunostaining was also done by the ABC kit from Dako Japan. The resting astrocyte under normal condition was not stained by calbindin antibody. Although the reactive astrocyte was observed by GFAP staining from 2 or 3 days after lesion, the calbindin-reactive astrocyte appeared from 3 to 4 weeks after lesion. It was also determined that not all GFAP-stained reactive astrocytes were stained by calbindin antibody. The numbers of stained reactive astrocytes by calbindin were increased until 6 weeks after ischemia and/or electrical lesion. A physiological role is still not clear, but calbindin may be expressed in some type of astrocyte and have some role in the differentiation of the glial cell.