Non-linear dielectric spectroscopy is a novel technique for determining the activity of (predominantly) membranous enzymes as their ability to generate harmonics when excited with a sinusoidal electrical field. In washed suspensions of yeast cells, the ability to generate harmonics is inhibited by low concentrations of sodium vanadate, suggesting that the vanadate-sensitive H(+)-ATPase is the major source of the non-linear dielectricity. This conclusion is greatly strengthened by the demonstration herein that the generation of harmonics by a strain containing a vandate-resistant H(+)-ATPase is also highly resistant to sodium metavanadate.