Transgenic mice overexpressing either the mouse γ2L or γ2S subunit of the GABAA receptor were generated in a C57BL/6 J × DBA/2 J mixed background and expanded into transgenic lines. Transgenic mice and littermate controls were analysed with respect to altered behaviour indicative of anxiety, motor activity and acute effects of benzodiazepines and alcohol, as well as with regard to altered responses to alcohol withdrawal and acute functional tolerance to alcohol. Biochemical tests assessed flunitrazepam- and ethanol-enhanced 36Cl– flux stimulated by muscimol in cerebellar and cortical microsacs and [3H]-flunitrazepam binding to cerebellar membranes. There were no significant differences in any of these measures between the transgenic and control mice, except in tests of acute functional tolerance to acute injection of ethanol. Compared to controls, mice carrying either the γ2L or γ2S transgene developed significantly less tolerance to the ataxic effects of ethanol. We conclude that acute functional tolerance to ethanol is very sensitive to the amount of GABAA receptor γ2 subunit available (regardless of whether it is γ2L or γ2S) but overexpression of neither subunit isoform alters other behavioural and biochemical phenotypes.