Two forms of the GABAA receptor gamma 2-subunit, named short (gamma 2S) and long (gamma 2L), and generated by alternative RNA splicing, have been identified in mammalian brain by molecular cloning techniques. We have produced antibodies against a synthetic peptide containing the 8-amino acid insertion present in the long form but not in the short one. Using the antipeptide serum, we have identified the gamma 2L subunit in membrane preparations of GABAA receptors from rat and mouse cerebellum and its cellular location in cerebellum.