Effects of amphiphilic derivatives of glycine esters of the general formula (CH3)3N+CH2COOCnH2n+1Cl‐ (n = 10, 12, 14, 16) on membrane potential and conductance in internodal cells of the algaNitellopsis obtusawere studied. The compounds decreased the potential difference between vacuole and external medium and increased the electric conductance. The effects depended on the length of the alkyl chain (n) and the concentration of these quaternary ammonium salts. Light‐induced hyperpolarization was suppressed by the salts. We suggest that the ammonium salts inhibit the electrogenic proton pump in the plasmalemma and enhance the passive efflux of Cl‐ from the algal