The expression of eight messenger RNA splice forms encoding the Flip and Flop variants of AMPA receptor subunits GluR-A to -D in the rat lumbar spinal cord was examined by in situ hybridization using specific oligonucleotides. In the dorsal horn (laminae I, II and III) the predominant mRNA was GluR-B Flip. Much lower levels of GluR-A Flip were found in lamina I and in superficial parts of lamina II outer. In the ventral horn, motor neurons expressed mainly GluR-B Flip, GluR-C Flip and Flop, and GluR-D Flip. Serial sectioning through large motor neurons indicated that a given cell contained, for example, both GluR-C Flip and Flop splice types.