A trpE-fusion protein containing a C-terminal sequence of a rat metabotropic glutamate receptor, mGluR5, was used to produce an antibody. On immunoblot, the antibody specifically reacted with mGluR5 expressed in mammalian cells and rat brain. Immunohistochemical analysis revealed intense mGluR5-like immunoreactivity (LI) in the olfactory bulb, anterior olfactory nuclei, olfactory tubercle, cerebral cortex, hippocampus, lateral septum, striatum, nucleus accumbens, inferior colliculus, and spinal trigeminal nuclei. The distribution pattern of mGluR5-LI corresponds very well with that of mGluR5 mRNA. Electron microscope analysis of the striatum revealed dense accumulation of immunoreaction products in dendrites which were often provided with asymmetrical synapses. These results suggest that mGluR5 is predominantly located in postsynaptic elements.