Myocyte-specific enhancer binding factor 2C (MEF2C) activates transcription by binding to the myocyte-specific enhancer binding factor 2 (MEF2) regulatory element and has been shown previously to be expressed in muscle and in the brain. We have now studied MEF2C expression in human brain using an antiserum raised against amino acids 140-238 of MEF2C. Western blotting demonstrated that, in fetal brain, MEF2C-immunoreactive bands have the same apparent molecular weight as those in extracts of COS cells transfected with MEF2C complementary DNA. In adult brain, however, MEF2C-immunoreactive bands have a higher molecular weight. In the cerebral cortex, MEF2C immunoreactivity is present in the cortical plate, and is not found in the intermediate zone or ventricular zone. At 14 weeks of gestation, the earliest age examined, MEF2C immunoreactivity is present in cell nuclei throughout the cortical plate. Subsequently, MEF2C immunoreactivity develops a bilaminate and then a trilaminate distribution, and ultimately is expressed preferentially in layers II, IV and VI of mature neocortex. MEF2C immunoreactivity is also found in entorhinal cortex, hippocampus, claustrum, cerebellum and amygdala, and in scattered cells in the thalamus. These findings suggest a role for MEF2C in postmitotic neuronal differentiation, in particular, in the development of certain cortical layers, but also in differentiation of other neurons as well.