Utilizing a basolateral membrane vesicle preparation containing Cl⁻-ATPase from Aplysia foregut, it was shown that orthovanodate inhibited Cl⁻-ATPase activity, ATP-dependent Cl⁻ transport and ATP-dependent membrane potential change. N-ethylmalemide (NEM) and p-chloromercurobenzoate (PCMBS) also inhibited the Cl⁻ pump biochemical and transport characteristics. However, bafilomycin, azide, DCCD or efrapeptin had no effect on the Cl⁻ pump characteristics suggesting that this Cl⁻ pump was a P-type ATPase.