Background. Menthol, a naturally occurring compound in the essential oil of mint leaves, is used for its medicinal, sensory and fragrant properties. Menthol acts as an agonist at transient receptor potential (TRPM8 and TRPA1) channels and as an allosteric modulator of several voltage- and ligand-gated ion channels, including recombinant GABA_A receptors. Here, we examined the actions of menthol on GABA_A receptor-mediated synaptic transmission in intact midbrain slices. Methods. Whole cell voltage-clamp recordings were made from periaqueductal grey (PAG) neurons in midbrain slices to determine the effects of menthol on GABA_A receptor-mediated phasic inhibitory postsynaptic currents (IPSCs) and tonic currents. Results. Menthol (150 – 750 µM) produced a concentration-dependent prolongation of spontaneous GABA_A receptor-mediated IPSCs, but not non-NMDA receptor-mediated excitatory postsynaptic currents (EPSCs) throughout the PAG. Menthol actions were unaffected by TRPM8 and TRPA1 antagonists, tetrodotoxin or the benzodiazepine antagonist, flumazenil (10 µM). Menthol also enhanced a tonic current, which was blocked by the GABA_A receptor antagonists picrotoxin (100 µM), bicuculline (30 µM) and Zn²⁺ (100 µM), but unaffected by the GABA_A antagonist gabazine (10 µM) or the GABA_C antagonist TPMPA (50 µM). In addition, menthol potentiated currents induced by the δ subunit-containing GABA_A receptor agonist THIP (10 µM). Conclusions. These results suggest that menthol positively modulates both synaptic and extrasynaptic populations of GABA_A receptors in native PAG neurons. Potentiation of δ subunit-containing GABA_A receptor activity in the midbrain, as well as other CNS regions, may play an important role in the behavioural effects of systemic or central administration of menthol.