The ion distribution in the vas deferens of the guinea-pig was determined following reserpine treatment and decentralization, procedures known to increase the sensitivity of this muscle to drug stimulation.2. There were no significant changes in the estimated intracellular ion concentrations following the two procedures. The half-times of (42)K and (36)Cl effluxes were also unaltered.3. As far as ion content is concerned there is no basis for suggesting an altered resting membrane potential in supersensitive smooth muscle.