Two polyclonal antibodies were raised against the gamma 1-subunit of gamma-aminobutyric acidA (GABAA) receptors. One of these antibodies could be used for the immunopurification of GABAA receptors containing gamma 1-subunits. These receptors exhibited [3H]muscimol and [3H]flunitrazepam binding, and their benzodiazepine binding properties were dramatically different from those of receptors precipitated by anti-gamma 2- or anti-gamma 3-antibodies. Western blot analysis of the immunopurified GABAA receptors indicated that the gamma 1-subunit exhibits an apparent molecular mass of 45-51 kDa. Furthermore, in addition to gamma 1-subunits, beta 2/3-, alpha 1-, alpha 2-, alpha 3-, and alpha 5-subunits could be detected in immunoaffinity column eluates from total brain. In contrast, gamma 2- or gamma 3-subunits could not be identified in GABAA receptors immunopurified by anti-gamma 1-antibodies. Similarly, gamma 1- and gamma 3-subunits or gamma 1- and gamma 2-subunits could not be identified in GABAA receptors purified by anti-gamma 2- or anti-gamma 3-antibodies, respectively. These data seem to indicate that GABAA receptors contain only a single type of gamma-subunit.