A unique segment of chicken GABAA receptor alpha 1 subunit was expressed in E. coli and used to generate an antiserum 2A specific for the subunit. The DNA fragment encoding the segment of alpha 1 was obtained by selective amplification by polymerase chain reaction (PCR) from a chicken brain cDNA library. The antiserum is characterized by its capacity to immunoprecipitate a [3H]flunitrazepam binding protein of 50 kDa, the chicken GABAA receptor alpha 1 subunit. Subsequent immunoblotting and immunocytochemistry analyses reveal that alpha 1 is expressed in the optic tectum and cerebellum as early as embryonic day 15 (E15), in various areas of telencephalon as early as E20 and distributed heterogeneously among different cell types. The early expression of alpha 1 may imply its functional significance in neurotransmission.