A novel subunit of the ␥-aminobutyrate, type A (GABA A ) receptor family has been identified in human and rat tissues. The subunit displays 30 -40% amino acid identity with known family members and represents a distinct subunit class (termed ). Transcripts of the subunit were detected in several human tissues and were particularly abundant in the uterus. The subunit protein can assemble with known GABA A receptor subunits and confer unique ligand binding properties to the recombinant receptors in which it combines. Most notably, the presence of the subunit alters the sensitivity of recombinant receptors to the endogenous steroid, pregnanolone. Identification of the subunit indicates a new target for pharmacological manipulation of GABA A receptors that are located outside of the central nervous system.