GABA A receptors (GABA A Rs) have long been a focus as targets for alcohol actions. Recent work suggests that tonic GABAergic inhibition mediated by extrasynaptic ␦ subunit-containing GABA A Rs is uniquely sensitive to ethanol and enhanced at concentrations relevant for human alcohol consumption. Ethanol enhancement of recombinant ␣43␦ receptors is blocked by the behavioral alcohol antagonist 8-azido-5,6-dihydro-5-methyl-6-oxo-4H-imidazo[1,5-a][1,4]benzodiazepine-3-carboxylic acid ethyl ester (Ro15-4513), suggesting that EtOH/Ro15-4513-sensitive receptors mediate important behavioral alcohol actions. Here we confirm alcohol/alcohol antagonist sensitivity of ␣43␦ receptors using human clones expressed in a human cell line and test the hypothesis that discrepant findings concerning the high alcohol sensitivity of these receptors are due to difficulties incorporating ␦ subunits into functional receptors. To track ␦ subunit incorporation, we used a functional tag, a single amino acid change (H68A) in a benzodiazepine binding residue in which a histidine in the ␦ subunit is replaced by an alanine residue found at the homologous position in ␥ subunits. We demonstrate that the ␦H68A substitution confers diazepam sensitivity to otherwise diazepam-insensitive ␣43␦ receptors. The extent of enhancement of ␣43␦H68A receptors by 1 M diazepam, 30 mM EtOH, and 1 M -carboline-3-carboxy ethyl ester (but not 1 M Zn 2ϩ block) is correlated in individual recordings, suggesting that ␦ subunit incorporation into recombinant GABA A Rs varies from cell to cell and that this variation accounts for the variable pharmacological profile. These data are consistent with the notion that ␦ subunit-incorporation is often incomplete in recombinant systems yet is necessary for high ethanol sensitivity, one of the features of native ␦ subunitcontaining GABA A Rs.