Alcohols and other anesthetics interfere with the function of a variety of systems regulated by guanosine triphosphate (GTP)-binding proteins (G proteins). We examined the effect of hexanol on the activity of the a subunit (Gαi1) of heterotrimeric G proteins. The GTP hydrolysis activity of recombinant Gαi1 was 0.029 mole Pi · mole Gαi1-1 · min-1 and was inhibited by hexanol at concentrations larger than 10 mM, with a 50% inhibitory concentration of 22 mM. Circular dichroism spectroscopy revealed that hexanol decreased the denaturation temperature of Gαi1 from 47.2°C to 42.5°C without altering its secondary structure at 10°C. Hexanol (30 mM) reduced the amount of monomeric Gαi1 in solution measured by size-exclusion chromatography, indicating that hexanol caused protein aggregation. However, the rate of GTPγS binding to Gαi immunoprecipitated from airway smooth muscle membranes was not affected by 30 mM hexanol. Excluding the apparent inhibition of recombinant Gα i1 resulting from aggregation-induced artifact, we found no evidence that the hexanol-induced inhibition of receptor-activated Gα i-coupled pathways in intact airway smooth muscle resulted from direct inhibition of the intrinsic rate of [35S]GTPγS binding to Gαi.