Conductance of gap junctions in many preparations has been shown to be sensitive to cytoplasmic pH, decreasing as pH decreases below 7.5 in fish and amphibian embryos and below 7.1 in crayfish septate axon. We have found a new class of compounds, benzyl acetate derivatives, that reversibly decrease junctional conductance, g(j), when applied in low concentration (~ 1 mM). Simultaneous intracellular pH (pH(i)) measurements show that the ester effects are attributable to reduction in pH(i). The sensitivity of g(i) to these compounds and the relative lack of side effects make these agents attractive for studies of the role played by gap junctions in normal tissue function. In addition, the finding of cytoplasmic acidification in response to cell exposure to esters suggests caution in interpretation of results obtained using esterified compounds for intracellular loading.